MONOGENETIC TREMA TODES THEIR SYSTEMATICS AND PHYLOGENY by B. E. Bychowsky English Editor WILLIAM J. HARGIS, JR. , NINTH TRANSLATION OF A RUSSIAN MONOGRAPH \ ,n a SERIES x= 5= ^^ or 1 tr . r-=l i ru i -D i in ^ CD = m = □ Monogenetic Trematodes Their Systematics and Phylogeny AKAAEMM5I HAVK CCCP aooAoriiHECKnn iihcthtvt B.E.BblXOBCKMM MOHOrEHETMqECKME COCAAbUJMKM MX CMCTEMA M (DMAOFEHMH ^^ M 3 AATE A b CTB O AKAAEMMM HAVK CCCP MOCKBA-AEHMHrPAA 19 5 7 Monogenetic Trematodes Their Systematics and Phylogeny by BORIS E. BYCHOWSKY Edited by WILLIAM J. HARGIS, JR. Translated by PIERRE C. OUSTINOFF AMERICAN INSTITUTE OF BIOLOGICAL SCIENCES 2000 P Street, N. W. Washington 6, D. C. © Copyright 1961, by AMERICAN INSTITUTE OF BIOLOGICAL SCIENCES First Printing, December 1961 Second Printing, August 1962 Library of Congress Catalog Card Number: 61-18229 printed in the united states of america by Graphic Arts Press, Inc. washington, d. c. Preface to Translation Translation of this monograph, undoubtedly the most valuable one written to date on this group of parasites, was undertaken as part of a long-term research project on the systematics, host-speciflclty and zoogeography of mono- genetic trematodes. ^ Translation and editing were accomplished in the following manner: 1. Having previously checked difficult words, Oustinoff read sight translation to Hargls. 2. Hargis, partially editing, wrote translation in long hand. 3. Hargis and Oustinoff edited this manuscript and Hargls put translation on tape. 4. Miss Conner transcribed translation from tape to first typescript. 5. Hargis edited typescript again. 6. Miss Conner retyped. 7. Hargls and Oustinoff re -edited by comparing typescript with book for content. 8. Typescript retyped by Miss Conner. 9. Dr. and Mrs. Oustinoff re -edited against text. 10. Hargls again edited typescript for final corrections. This project, begun in September of 1958, has taken over two and one -half years to complete. A conscious effort has been made to keep this translation as near the original as possible. It Is probably Inevitable, however, that some of the nuances of meaning In the original have been distorted or lost. For this we apologize to Dr. Bychowsky and the reader. Virginia Institute of Marine Science Translation Series, Number 1. 2 Translation and editing supported by funds from Grant No. E-2389 of the National Institutes of Health. Publication under auspices of AIBS Translation Series supported by Grant No. G14802 from the National Science Foundation. 3 Chairman, Department of Modern Languages, College of William and Mary, Williamsburg. V Certain passages were difficult to translate. Most troublesome were: saiCOHOMepHOCTB % which literally is "lawful measure" but which may be translated variously as- -conformity with law, regularity, principle, normality; and sepKaJbHUfi , which is translated as smooth or bilaterally symmetrical. In the case of the former word, several alternative translations are usually given where it occurs in the text. Where a different English phrase seems to fit Dr. Bychowsky's meaning better or serves to clarify the text, it has been inserted in parentheses with the Latin notation nobis- -by us. To avoid lengthy rendition of the original, we have at times used new words the meaning of which seems, nevertheless, clear. For instance, we have translated mnogoletnil by polyannual to designate a cycle which lasts many years, and segoletki by young of the year to designate fishes which are less than one year old. Certain obvious errors or misspellings in the original text were changed, less obvious ones are noted with (si£). The bibliography was divided into two parts, Russian and non-Russian, in the original and has been retained that way in the translation. The Library of Con- gress system for the spelling of the names of Russian authors has been followed In the bibliography. When the name of the author was spelled differently in a previous translation, the alternate spelling follows our transliteration. The reason for this is that for purposes of research it is preferable to follow the system of the Library of Congress which indicates variant spellings. To prevent misunderstanding which may have arisen from the preserva- tion of Russian letters used In the original to Identify the drawings, we replaced, in the translation, Russian letters by those of the English alphabet, for instance, Russian B by English C, etc. To clarify further this substitution, we have reproduced on page iv both alphabets. In so doing, we do not think It out of place to include in parentheses after Russian letters the symbols used for their transliteration. The numerals between the alphabets indicate the relative place of each letter in Its respective alphabet. Though the Latin morphological terms are not italicized in the Russian text, we prefer to do so in the translation. For convenience in referring to the Russian text the original pagination is given in the margin of the translation opposite the place where the new page begins. Occasionally figures or tables are somewhat displaced from their original page loca- tion; however, since they, themselves, are numbered sequentially, no confusion should result. VI The citation of numbers for measurements and numbered structures are generally given in the translation as they were in Professor Bychowsky's book. This should further facilitate checking with the Russian. Aside from the fact that the text is occasionally interlarded with references to dialectical materialism which seems to have little place in this or any other scientific paper. Dr. Bychowsky has produced the best, most comprehensive treatise on monogenetlc trematodes ever offered to science. Besides being an excellent account of the biology and systematlcs of these interesting parasites, the sections on host-parasite relationships and the historical aspects of the general phenomenon of parasitology are noteworthy. Bychowsky's determinations of the phylogenetlc relationships among and between the parasitic groups of the Phylum Platyhelmlnthes and the free -living turbellarians are extremely Interesting. Thus, though the book is devoted chiefly to the Class Monogenoidea (Beneden) Bychowsky, 1937, It is a significant contribution to all parasitology. Thanks are due to Miss Patricia R. Conner of the Virginia Institute of Marine Science who transcribed, typed, and assembled the manuscript, and to Mrs. Ellen Oustinoff, who assisted with final editing. William J. Hargls, Jr. Laboratory Director and Dean School of Marine Science of the College of William and Mary in Virginia VII ALPHABETS Russian English A a(a) 1 A a B d(b) 2 B b B B(v) 3 C c r r(g) 6 D d R fl(d) 5 E e •ii"' 6 7 F f G g 3K H(2h) 7 8 H h 3 3(2) 8 9 K k M H(i) 9 10 L 1 11 fi(t) 10 11 M m K K(k) 11 12 N n JI JI(1) 13 15 M M(in) 13 14 P P H H(n) 14 15 Q a 0(0) 15 16 R r n n(p) 16 17 S s P p(r) 17 18 T t C C(s) 18 19 U u T T(t) 19 20 V V y y(u) ^ $(f) 20 21 W w 21 22 X X X x(kh) 22 23 Y y i^ ^(ts) 23 24 Z z ^ ti(ch) 24 ni ra(sh) 25 m IH(shch) 26 '* tV) 27 H(y) 28 hin 29 3 3(e) 30 K) K)(fu) 31 fl fl(fa) 32 * As a rule, e* occupies the same place as e in Russian alphabet . ** The hard sign (") is used only in the middle of a word, VIII The American Institute of Biological Sciences And What It Does American biologists, seeking to harness pressure for modernization and coordination, created the American Institute of Biological Sciences to administer programs in behalf of all biology. Protection of traditional areas of concentration has remained inherent in the Institute, although it serves all disciplines. Scientists in research, teaching or applied fields may propose and sponsor creative exploration of frontier areas or search for solutions to perennial problems. Through the Institute, too, biologists stimulate scholarly and admin- istrative interchanges of current information. Last year more than 800 biologists found their professional life enriched and their personal satis- factions deepened by active participation in AIBS-managed undertakings. Biologists now direct more than 100 separate Institute projects. Some are massive, long-term concerns with the future of science, such as the Biological Sciences Curriculum Study and the Biological Sciences Communi- cation Project. Others are short-lived but productive attacks on vital spe- cific targets. Through steadily Increasing resources, the AIBS provides sound, full-time management for biology -centered activities. Among these are advance preparation and operation of conferences and symposia, enlisting and attracting public and private understanding and support, placement services for individual biologists, and translation, publishing, editorial and business services for learned societies. In these and other ways, AIBS "minds the store" and serves as the eyes, ears, voice and strong right arm of 85, 000 professional biologists In this country and around the world. IX TABLE OF CONTENTS Page FOREWORD . . INTRODUCTION XV xvii PART I MORPHOLOGY AND BIOLOGY OF MONOGENETIC TREMATODES CHAPTER I. Morphology of Monogenetic Trematodes 3 CHAPTER II. Biology of Monogenetic Trematodes 71 CHAPTER III. Embryology of Monogenetic Trematodes 85 CHAPTER IV. Life Cycles of Monogenetic Trematodes 108 SUPPLEMENT. Materials on Embryology of Monogenetic Trematodes 146 PART II OCCURRENCE OF MONOGENETIC TREMATODES ON THEIR HOSTS CHAPTER I. Hosts of Monogenetic Trematodes 239 CHAPTER II. Occurrence of Species of Monogenetic Trematodes on the Species and Genera of their Hosts --Fishes. 242 CHAPTER III. Occurrence of Genera of Monogenetic Trematodes on the Families and Orders of their Hosts--Fishes. 280 CHAPTER IV. Occurrence of Families of Monogenetic Trematodes on Orders of their Hosts--Fishes. 308 CHAPTER V. Occurrence of Monogenetic Trematodes among Amphibia and Reptilia 320 CHAPTER VI. Certain General Considerations about Occurrence and Specificity 325 CHAPTER VII. Fauna of Monogenoidea of Separate Groups of their Hosts. 347 81476 XI PART III SYSTEMATICS AND PHYLOGENY OF Page MONOGENETIC TREMATODES CHAPTER I. Basic Trends and Phylogenesis of Monogenetic Trennatodes 377 CHAPTER II. Brief Summary of the System of Monogenetic Trematodes. 392 CHAPTER III. System of Monogenetic Trematodes 404 Class Monogenoidea Subclass Polyonchoinea Order Dactylogyridae Suborder Dactylogyrinea Family Dactylogyridae Family Diplectanidae Family Protogyrodactylidae Family Calceostomatidae Suborder Monopisthocotylinea Family Monocotylidae Family Loimoidae Family Dionchidae Family Capsalidae Family Acanthocotylidae Family Microbothriidae Order Tetraonchidea Family Tetraonchidae Family Amphibdellatidae Family Tetraonchoididae Family Bothitrematidae Order Gyrodactylidea Suborder Gyrodactylinea Family Gyrodactylidae Suborder Polyopisthocotylinea Family Polystomatidae Family Sphyranuridae Subclass O 1 ig o n c h o i n e a Order Diclybothriidea Family Diclybothriidae Fanaily Hexabothriidae Order Chimaericolidea Family Chimaericolidae Order Mazocraeidea Suborder Mazocraeinea Family Mazocraeidae Family Hexostomatidae XII Page Suborder Discocotylinea Family Discocotylidae Family Anthocotylidae Family Plectanocotrylidae Family Diclidophoridae Family Microcotylidae Family Protomicrocotylidae Family Gastrocotylidae CHAPTER IV, Phylogenetic Interrelations of Families of Monogenetic Trematodes 538 CHAPTER V, About Certain General Peculiarities of Phylogenetic Development of Monogenetic Trematodes 552 CHAPTER VI. Position of Monogenetic Trematodes in the System of Flat Worms 563 CONCLUSION 573 LITERATURE CITED 577 ALPHABETICAL INDEX OF NAMES OF MONOGENETIC TREMATODES 613 ALPHABETICAL INDEX OF NAMES OF HOSTS OF MONOGENETIC TREMATODES 622 XIII Page Numbers In Margins Refer To Original Russian Text XIV FOREWORD Within the last 20 to 25 years an increasing nunaber of works have p. 3 been devoted to the monogenetic trematodes. Despite this, our knowledge is still far behind that of other parasitic groups, particularly digenetic tre- matodes and tapeworms. For this reason I consider it my duty to publish the results of my almost 30 years of research in the field of phylogeny and systematics of the Monogenoidea considering that, despite the numerous and irritating gaps which are clearly apparent to me, my work nevertheless will be fruitful in the development of further research in this very interesting group in the practical as well as the theoretical sense. I am prompted to this publication by the memories of constant and friendly exhortations of my teacher, Valentine A. Dogiel, whose desire it was to see this work completed. V. A. Dogiel was vitally interested in these questions which inspired me, and much of what is written here is the result of mutual discussion and lively disputation which took place during all the years of our common work, beginning with the expedition to the Aral and Caspian Seas in 1930-32, It is impossible to express with words the feeling of gratitude which I experienced when I remember and evaluate the influence of V. A. Dogiel on my life and scientific work. The completion of the present research was greatly impeded by the fact that, until recently, I could only work sporadically because of the overload caused by other duties. Consequently, a warmer feeling comes from the remembrance of constant help and friendly attention which was given my by my friends in the Department of Parasitology and the Ichthy- ology Laboratory of the Zoological Institute of the Acadenay of Sciences, U. S. S. R. I also received considerable help from collaborators of the Laboratory of Fish Diseases, VNlORKh (AU-Union Scientific Research Institute of the Fish Industry of Lakes and Rivers riobis ) and the Depart- ment of Invertebrate Zoology of Leningrad University. Academician E. N. Pavloski, showed constant attention to my work, and he often helped to organize many of my field trips. ,^ i During the writing of this work I received great support from two 1 of my friends, A. A. Strelkow and A. S. Monchadsky without whose help my p. 4 'I work would have remained unfinished for a long time. Their friendly criticism and advice constantly helped my work. I must also mention the help of A. A. Strelkow and many of our common field trips to the Pacific Ocean, the Sea of Japan and the Sea of Okhotsk. The shaping up of this work, which required great labor, was accomplished with the collaboration of L. F. Nagibina. The majority of the original drawings were made by her. In addition to that, for many years L. F. Nagibina constantly helped me in my experiments and field XV trips. The final processing of the drawings was made by the brigade of artists of the Zoological Institute, primarily by N. Liahovi and E. D. Samenskia. I beg all my friends who cooperated in my work to accept my heart- felt gratitude. All the drawings which illustrate the present work were nriade from the ventral views of the whole mounts of the worms. The exceptions are de- scribed in the legends. Borrowed drawings are acknowledged with references to the author and the year of publication. The references to location of hosts of monogenetic trematodes are made in the legends of the drawings to permit verification of the correctness of classification, and also in this connection because many of these references will widen the scope of the information about the widespread locations of the hosts of the different types of parasites. The work was completed in December 1955, and all the literature available to me which had been published up to the middle of 1955 was utilized for it. Unfortunately, certain important works were known to me only by abstracts. Likewise, I was unable to include those papers which appeared during the year and a half which passed from the time of completion to the time of publication. In doing so I missed a certain number of references which cited new data concerning the distribution and biology of monogenetic trematodes, and also which described certain new types and species. The inclusion of all of these references in the present work was impossible. Comnnents on more important publications were added during the course of reading the proofs, but only as special footnotes. Nevertheless, I believe the existing irritating omissions will not seriously influence the basic con- clusions. B. Bychowsky XVI INTRODUC TION Our first observations on the monogenetic trematodes were begun P- "^ during student years at the Institute of Natural History in Peterhof, when in 1927 we became acquainted with the morphology and growth of a series of representatives of the species of Dactylogyrus Diesing and later the poly- stomes of the frog. The striking resemblance of the larvae of these two groups, despite the great dissimilarities of the adults, forced us to consider the question of family relationships within the limits of the group of the monogenetic trematodes even then. Further work on parasitic worms led to the firm conviction of the necessity for special research on the subjects of phylogeny and interrelation- ships of the parasitic flatworms. At the same time, the first studies of the monogenetic trematodes convinced us of the essential significance of this group to an understanding of the phylogenies of all of the groups of parasitic worms. Already in 1932, while examining the interrelationships of the vari- ous species of Gyrodactylus von Nordmann and Dactylogyrus Diesing, we came to the conclusion that it is impossible to understand systematic relation- ships and phylogeny without careful study of the embryological development of monogenetic trematodes, because, in a number of cases the true relation- ships are masked by the resemblances of the adults which are connected with the analogous conditions for existence. About 1935-36 we were convinced of the incorrectness of the wide- spread view concerning the close kinship between monogenetic and digenetic trematodes, and the monolithic relationship of the group of Cestodaria, and in 1937 we published a work containing an effort to build a system of parasitic flatworms on the basis of the scheme of their phylogenetic interrelationships. This work was primarily preliminary in character because of the insufficiency of factual material. Its publication forced us to pay more attention to the questions of the interrelationships within the class Monogenoidea, inasmuch as it seemed to us that the analyses of these interrelationships would give a more solid base to our entire system. Henceforth, we set for ourselves a problem of studying all aspects of the monogenetic trematodes for the purpose of re-establishing the phylogenesis of the given group and a thorough treat- ment of its systematics. The study of the interrelationships of many contemporary inverte- p. 6 brates, particularly the worms, presents considerable difficulties because of the absence of fossil remains. As a result, the researcher who is interested in phylogeny is faced with the difficult problem of reconstructing historical processes on the basis of materials dealing with the morphology and life history of contemporary animals. The method of mutual verification of data from the studies of different phenomena of the group under study allows us to XVII reconstruct its past and those genetic links which can be utilized for the building of the system on phylogenetic foundations with a high degree of reliability. It is impossible not to note that parasitic animals are more con- venient in this connection because tneir examination provides supple- mentary, purely parasitic criteria for the reconstruction of the past history of the group. It seems to us that the importance of the study of phylogenesis of any given group of animals must not be underestimated. Only the concrete knowledge of the phylogenesis of separate groups permits us to represent in an accurate way a general nature of the evolution of the animal world which has great theoretical significance and which also appears as a basis for the exact classification of animals. Along with this, we are firmly con- vinced that only an adequate, complete knowledge of the phylogenesis of a gr up can serve as the sufficient basis for the solution of natural methods of its full economic utilization. As applied to the parasitic animals, the know- ledge of phylogenesis of a group is indispensable for the correct planning of methods of biological struggle with parasitic diseases, and also for a clear understanding of the potential danger of any single group of parasites or of a specific parasite fauna. Our research on phylogenesis of parasitic flatworms rs still far from complete, but it is already possible to expediently sunn up the study of phylogenetic relationships of monogenetic trennatodes and also to build a system of the group on the basis of these interrelationships. Our present wOrk is dedicated to these two problems. Data from the literature and new material collected by us, our students, and colleagues forms the foundation of our system. In many instances the published data, to our regret, are entirely unsatisfactory because the authors did not pay proper attention to certain peculiarities of morphology and embryology which, from our point of view, have the great- est significance. This forced us to re-examine or repeat the experiments which was extremely burdensome because of the difficulty of securing original material. For these basic reasons we were forced to consider with extreme care the data pertaining to the discovery of a particular species of monogenetic trematodes on a particular host. One of the reasons is the in- exactitude in identifying the host or parasite. The second, much more com- p. 7 plex, precisely the (reporting of a, nobis ) finding of a parasite not on the host peculiar to it in normal conditions, but on the strength of local discovery of the host during the examination or during the capture of the fish host (in the instruments of capture of the fish or during the transport) when a mechanical transfer or an independent transfer from one host to another might occur. The third and most important reason, which in numerous cases demands special analysis, involves the description of a parasite from a host which is not habitual to it as a result of the grouping for varying periods XVIII of time of different species of fishes (mainly in fresh water or in naarine display aquaria). We will consider the cases which can be explained by the various reasons later on, but here we must note particularly the necessity of very cautious treatment of the data of MacCallum, who worked in the New York Aquarium and who allowed great inaccuracies to creep into his research. Systematic and morphological collections of monogenetic trematodes and research with live animals provided the material for this work. The collections of monogenetic trematodes were conducted either by us directly at the place of location of the live hosts or under laboratory conditions from ichthyological collections chiefly from the Zoological Institute of the Academy of Sciences, U.S.S.R. All in all, the collections contain very significant ma- terial from the most diversified regions of the Soviet Union and foreign coun- tries. One must especially note material from all the South Seas of Russia, from middle Asia (Region Tschu and Tadjikistan and Turkmania and others), from the far East (Amur River System, the Sea of Japan, the Sea of Okhotsk and the Pacific Ocean), from Japan (fresh water and salt water), from the fresh waters of the Maylayan Archipelago, from the United States of America and Canada, and finally from western Europe (Mediterranean Sea, Atlantic Ocean and others). The smallest quantity of material was received from Africa, South America, and Australia. The study of live material was conducted by us in the Leningrad region (the Bay of Finland, River Neva and'Ropscha" Fish Farms, small lakes, ponds and brooks) in 1927-1929, 1931-1932, and 1945-1952; on White Lake in 1931; in Karelia (a system of lakes near Konchezero near Peltro- lavodsk) in 1932; on the Volga (near Kostroma and Saratov in the Delta) in 1926-27, 1931-32, 1947 and 1953-54; in western Siberia (Barabinskaya Steppe, lakes of the group of Chanov) in 1933; on the Black Sea (Karadag and Sebastopol) in 1927, 1935 and 1947; in the Sea of Azov (in the estuaries of Ahtarinsk) in 1933; the Caspian Sea (on the Island of Sara) in 1931-1932 and 1955; in the sea of Aralsk (Aralsk and Muynak and the islands of Uzun-Kair and Kuzdjk-Pes) in 1930; in Tadjikistan (in region of Stalinbad and Vahsha) in 1943-1945; on the Sea of Japan (the Bay of Peter the Great and the western banks of Sakhalin Island) in 1946 and 1949; on the Sea of Okhotsk (Bay of Aniv and the western Shore of Sakhalin) in 1946 and 1949; in the shallow waters of Kurile (in the Island of Shikotan) in 1949; and in the Pacific Ocean in 1955. For this work we also utilized the researches on live material P- ° which were conducted by colleagues of our laboratory: A. V. Gussew on Hanka Lake, 1948-1949 and in the Barents and Norwegian Seas in 1950; by U. A, Strelkow at the Sebastopol Biological Stations in 1949; and L. F. Nagibina in the Leningrad region in 1946-52; and N. A. Izumova on the Ropscha Fish Farm south of Leningrad in 1951 and 1952. XIX The researches on Monogenoidea were carried out in many different ways, from the point of view of biology, morphology and embry- ology. We gave special attention to wOrk on live materials because it was possible to discover a whole series of structures only in this fashion. Thanks only to the study of live materials was it possible to understand the physiological meaning of a series of morphological peculiarities unknown until the present time. We would also like to underline this circumstance On the strength of the fact that at the present time the study of monogenetic trematodes is based almost entirely upon fixed material which is completely wrong and in many cases leads to erroneous results. It is curious that the researches of the middle of the last century widely utilized live materials, and in many cases their works describe the forms and structure of mono- genetic trennatodes much more precisely than corresponding data of con- temporary authors who are armed with complete microscopic technology but who do not employ direct observation of living Organisms. Unfortunately, we could not utilize the data concerning geo- graphical distribution of monogenetic trematodes because there is still very insufficient data at the present time, and this could have led to faulty conclusions. However, in certain isolated cases distribution was taken into consideration. XX PART I MORPHOLOGY AND BIOLOGY OF MONOGENETIC TREMATODES Page Numbers In Margins Refer To Original Russian Text PART I MORPHOLOGY AND BIOLOGY OF MONOGENETIC TREMATODES CHAPTER I MORPHOLOGY OF MONOGENETIC TREMATODES The present chapter contains a description of the morphology of p. H monogenetic trematodes expressed in such a way as to serve as a basis for further considerations of the evolution of the group. In connection with this, not all parts are described with an equal degree of completeness, and on the other hand, the appraisal of such morphological characteristics is made from the point of view of the phylogenetic researcher and not of the (pure) morphologist. We shall also indicate that the material described has, itself, an independent significance, because neither in native nor in foreign litera- ture is there anything comparable at the present time. In Russian literature monogenetic trematodes^ which were sepa- rated by us into an independent class (Bychowsky, 1937), are considered with digenetic. trematodes. Consequently, as a result of the greater at- _ Referring to textbooks and morphological references, because in literature on systematics our system of parasitic flatworms is acquiring a greater number of adherents. tention to digenetic trematodes, the information on the morphology of the monogenetic trematodes is given in such a fragmented fashion that it com- pletely fails to impart an accurate impression concerning the group. Among foreign works the most solid description of monogenetic trematodes is the essay of M. Braun (Braun, 1889 to 1893) which became extremely antiquated although, in some respects, it preserves its signifi- cance even to the present time. The second among the essays is the work of O. Fuhrmann (Fuhrmann, 1928) very succinctly written by a non-specialist, and it also has become antiquated. During recent years there appeared two more essays concerning the group which interests us, one by Ben Dawes (Dawes, 1947) which is devoted to monogenetic and digenetic trematodes, the other by Nora Sproston (Sproston, 1946) which is devoted especially to mono- genetic trematodes. Both essays have sections on morphology, but they are extremely short and serve mainly as an introduction to the systenaatic parts. Abbreviated data on morphology of monogenetic trematodes are scattered in a considerable number of specialized works. The most im- portant are the researches by Zeller (Zeller, 1872-1876), Cerfontaine (Cerfontaine, 1814-1900), and Seitaro Goto (Goto, 1891 - 1917) who produced a series of very substantial works which contain a significant amount of morphological material along with their systematic material. Recently, Brinkmann (Brinkmann, 1940-1954) published a series of works which have significance for Monogenoidea and which are based, not only on external characteristics, but also on detailed mor- phological analyses of interior structures. 12 Literature data and especially the results of personal research were utilized for the present essay. Sizes. In the majority of cases the sizes of the monogenetic trematodes usually vary between the lengths of 0. 03 to 20 mm, and only in rare cases do they reach a larger size. Thus Capsala martinieri Bosc (Fig. 1) reaches 30 mm in length and 25 mm in width, Squalonchocotyle sonnniosi (Causey) has a length of about 25 mm and probably Sq. borealis (Beneden) (Fig. 2) reaches up to 30 nam, etc. One can consider it a general Fig. 1, Capsala martineri Bosc, adult worm. (According to Price, 1939). rule that marine forms are larger than fresh-water forms. It is necessary, however, to note that the naeasurement of size is hampered by the fact that the body of monogenetic trematodes is capable of contracting and stretching excessively. Most of the species can stretch almost tvice, and contract as much in relation to the normal condition of their bodies. Thus, Dactylogyrus auriculatus (Nordmann) (Fig. 3) which is about 0. 5 mm in the normal state can stretch to 1 . 2 mm and contract to 0. 3 mm. Shape of the Body. Bilateral symmetry is the most common, with the longitudinal axis of the body with a narrowed and rounded an- terior end, and an adhesive disc on the posterior end which is more-or- less separated from the rest of the body. The ratio between the longi- tudinal and transverse axis fluctuates significantly in different species. For instance, certain individuals of Tristoma cdccineum Cuvier (Fig. 4) may be as wide as they are long, and the above mentioned Squalonchocotyle somniosi (Causey) has a length which exceeds the width by 11 times. The most common type is 3-4 times longer than wide, as for instance, with the majority of Dactylogyridae (Fig. 5). Along with these bilaterally sym- metrical species we also find asym- metrical species such as Vallisia striata, Perugia and Parona (Fig. 6), which shows lateral growth in the middle of its body that divides the body into two separate sections. The posterior section is strongly curved and unequally developed in relation to the longitudinal axis. Asymmetry of such a type is undoubtedly a second- ary phenomenon. There are also other types of asymmetry, also of secondary origin, but linked to a special type of evolution of the adhesive apparatus. The latter, in a series of cases, develops only from one side of the body, thus resulting in asymmetry, nevertheless the internal structures of the body re - main bilaterally symmetrical. In other cases, which are superficially similar but different in nature, asym- metry results from the displacement of the symmetrical adhesive disc to- ward one side of the body of the animal. Examples of asymmetry of the first type can be seen in representatives of the species of Gastrocotyle (Fig. 7) and the second type in the species of Axine (Figs. 8 & 9). p. 13 Fig. 2. Squalonchocotyle borealis (Beneden), adult worm from the gills of Somniosus microcephalus (Bl. and Schn. ) near the banks of Murman (Barents Sea) p. 14 ilMH Fig. 3i Dactylogyrus auriculatus (Nordmann), adult worms in various stages of contraction, f-rom gills of Abramis brama (L. ) from the Delta of the Volga. Fig. 4. Tristoma coccineum Cuvier, adult worm from the gills of Xiphias sp. from the region of the Maderia Islands (Atlantic Ocean). The transverse section of the body (Fig. 10) varies from a rounded shape (as for instance in a series of sections of Dactylogyrus) to one which is greatly flattened dorsoventrally (among representatives of the genus Nitzschia or Capsala). The ventral side of the body is usually slightly c-incave, and the dorsal correspondingly convex. a.iMn Fig. 5. Dactylogyrus vastator Nybelin, adult worms from the gills of Cyprinus carpio L. from Fd.^pshansk Ponds (Leningrad region) (According to Bychowsky, 1933). Fig. Vallisia striata Perugia and Parona, adult asymnietrical worm. Natural size 10 mm. (According to Monticelli, 1912). The lateral sides of the body are entire or smooth with few exceptions (see page 43 ). This smooth-margined condition does not pertain to the adhesive disc the sides of which can form an intricately cut figure. The orientation of the body of monogenetic trematodes does not offer any difficulty; their oral opening is, as a rule, terminally or subterminally located and the attachment apparatus is always at the posterior end. Color. The color is usually determined by the color of the in- ternal organs, but the body itself is either colorless or grayish white. Also, thanks to the organs showing through, the color may be rose, reddish, brownish, or even blackish (intestine), milk-white color (vitelline material, gonads), yellow color or tan (uterus). p. 15 o;« Fig. 7. Gastrocotyle trachuri Beneden and Hesse, adult worm from the gills of Trachurus trachurus (L. ) from the region of the Cape Verde Islands (Atlantic Ocean). Fig, 8. Axine belones Abild- gaard, adult worm from the gills of Belone belone (L. ) from the region of Sebastopol (Black Sea) Attaching Structure s. The anterior end of the body bears at- taching organs which serve mainly for the attachment of the anterior or head end during feeding, and also play an auxiliary role during the loco- motion of the animal. These organs can be divided into two main groups: those that are not connected to the mouth funnel or the oral aperture; and the second type, those that are connected to the niouth funnel or the oral aperture. 01mm Fig. 9. Axine sp. I, attaching disc (middle hooks of the larval disc are located almost in the middle of the common row of clamps). From the gills of Cypselurus sp. from the region east of the Japanese Islands (Pacific Ocean). i-'ifj, 10. Cross section of the body of A--Nitzschia sturionis (Abildgaard), B.- -Ancylodiscoides siluri Zandt. To the first group of anterior attaching structures are related the head papillae, the bothria, the little pits and suckers. The second group includes the buccal funnel, the pharyngeal sucker, and the buccal funnel suckers. In this connection the anterior end of the most primitive mono- genetic trematodes is sonnewhat flattened dorsoventrally , is rounded or p. 16 truncated, and the numerous ducts of the head glands open along its edge, apparently heterogeneous, but actually producing an agglutinating secretion which serves for the attachment for the anterior end of the body. In the majority of cases, in the forms which have as yet no differential growth of the anterior end of the body, the excretory ducts of the head glands are not located evenly along the entire anterior edge, but by groups of from 8 to 2 clusters (Fig. 11). In connection with this, we observe in a series of sections the formation of head organs the anterior end of which are in the form of more or less well-developed but always moving lobes. The The number of head glands is usually paired, from one (for instance Gyrodactylus , Fig. 12) up to 4 (for instance Murraytrema, Fig. 13). One often sees two pairs of head glands (for instance Dactylogyrinae , the p. 18 majority of Ancyrocephalinae and others--Fig, 5, 65 and others). Each head organ receives at its posterior end ducts of the clusters of head glands. As a rule, one cluster of ducts of head glands enters into one head papilla, nevertheless sometinnes a great number also enter a single head papilla depending upon an increasing size of the head papillae. The latter, in a series of cases; develop unequally so that two of them gradually pre- p. 19 dominate and the others disappear (for instance Diplectanum , Fig. 14). Next in complexity of the anterior attaching apparatuses are the attaching bothria. The latter have the appearance of two thickenings of the body symmetrically located on the sides of the anterior end and are weakly separated from it. The musculature of these head bothria is stronger than that of the head papillae and the head glands open into them with many individual ducts or by several clusters, (for example Emprutho- trema, Fig. 15), or equally spaced along its full length ( Dionchus , Fig. 16). It is absolutely clear that the head bothria represent the latest stage of morphological development of the head organs. Further, the process of complication involves increased musculature of head bothria, and its sepa- ration from the musculature of the body and the appearance of cup-like in- dentations on the external side of the bothria, which leads at first to the formation of head pits (for instance Nitzschia, Fig, 17), and also, during the following development (both in the phylogenesis and ontogenesis) leads to the forination of more or less strongly developed head suckers (for instance Tristoma, Fig. 4). As a rule there is one pair of head bothria or suckers (the following present exceptions: 1. The genera Bothitrema , the only species of which R. bothi (MacCallum) (Fig. 19) has, judging by the drawing and description of Price (Price, 1937b), four adhesive pits p. 20 on each side of the anterior end (see however page 396); and secondly, the genera Loimos and Loimosina (Fig. 20) in which the anterior end has four small head suckers. As for the head glands in adult forms, the 10 OOiMM Fig. 11.. Head end of the larva of an undetermined monogenetic tre- matode from the gills of Prognichtis agoo (Schl. ) near the Banks of Hokkaido (Pacific Ocean). O.fi, Fig. 12. Gyrodactylus elegans Nord.- mann, adult worms from the gills of Cyprinus carpio L. from pond farms in the region of Alma-ata (Kazak, SSSR). Fig. 13. Murraytrema robustum (Murray), adult worm. Natural size 2. 5 mm (According to Murray, 1931). nunaber decreases in proportion to the complication of the muscular attaching apparatuses (concerning the ones that are still developing, see the corres- ponding section of the book). 11 The second group of anterior attaching structures, as has been stated above, is associated with the oral aperture and the buccal funnel. Fig. 14. Diplectanuni similis Bychowsky, adult worm from the gills of Corvina nigra Cuv. and Val. from the region of Karadaga (Black Sea). Fig. 15. Empruthotrema raiae (MacCallum), adult worm. (According to Price 1938) Actually, we deal with two separate structures, to be more pre- cise with the changes in shape of the anterior end of the buccal funnel and with its suckers. In the simplest case the external edge of the buccal funnel serves for adhesion (for example Linguadactyle , Fig. 21). Further, we have all stages of transition to the formation of a more or less well-developed oral p. sucker around the oral orifice at the expense of the buccal funnel Squaloncho- cotyle. Fig. 2; Polystoma, Fig. 22). Apparently in unusual cases one of the edges of the mouth sucker can form a series a series of sucking pits, but in no case do they represent the transitional link to the following group. In other cases in which there are no changes in the external edge of the buccal funnel, which remains in its primitive state, on the internal surface of the funnel along its sides there begin to form two internal suckers which in various species reach differing degrees of attaching capabilities (Figs. 23,24). These suckers of the buccal funnel are not connected in origin with the other 21 12 head structures which serve for attachment, but represent formations pe- culiar to a large group of families of monogenetic trematodes Diclido- p. 2Z phoridae, Mazocraeidae, Microcotylidae, etc. , see the systematic sec- tion, page 402. One must note that in the work of Braun, mentioned in the beginning of this chapter, the author points to the principal distinction be- tween the first and second groups of the attachment organs of the anterior end of the body of these animals, saying that the former and the latter are in no way linked genetically, because sonne of thein appear as derivatives p. 23 Fig. 16. Dionchus agassizi Goto, youjig worm from the gills of Rernora remora (L. ) from the Indian Ocean. Fig. 17. Nitzschia sturionis (Abildgaard), adult worn"! from the buccal cavity of Huso huso (L. ) Island of Sara (Caspian Sea). of the exterior layers and others appear as derivatives of the layers limiting the buccal cavity. Unfortunately, this direct statement of Braun has not been sufficiently taken into consideration by specialists in the group and this oversight has led to connpletely arbitrary and wrong conclusions concerning the interrelations of the different systematic groups. 13 In order to complete the description of the anterior attaching apparatus, one must also note that the species that have apparatuses of the second type are also equipped with head glands which open by their ducts on the anterior edge of the body in a varying number of clusters, but inde- pendently of the buccal funnel and its derivatives. Thus, in Microcotyle they open by three clusters of ducts (in front and along the sides of the buccal funnel), in Octostoma by two clusters of ducts, etc. (see Fig. 23 and also the chapter on embryology). Fig. 18. A. Acanthocotyle williamsi Price, adult worm from the skin of Raja rosispinus G. and Town, near the eastern region of southern Sakhalin (Sea of Okhotsk); B. Enoplocotyle minima Tagliani, adult worm. (According to Tagliani, 1912). Natural size 0.4 mm. 14 Attaching Disc. The main attaching apparatus which is used for the fixation of the animal to the body of its host is a complexly arranged system of attachment organs lying on the posterior end of the body, which p. 2 u J3 ■4-> -i-l a M ■ iH PI O CO g u c en O O o h 2 O ^-\ •i-t . . d .-4 u o u u < a \ Fig. 46. Protoncyrocephalus strelkowi Bychowsky, adult worm from the gills of Limanda aspera (Pall. ) from the region of Yablochnoii (Southern Sakhalin, Sea of Japan), Fig. 47. Cathario - trema selachii (Mac- Callum), adult worm. (According to Price, 1938). As regards Polystomatidae , a powerfully developed disc more or less delineated from the body and provided with six suckers, 16 nnarginal or edge hooks and 2 to 4 middle hooks is characteristic. The latter can be absent (for instance in Neopolystoma, Fig. 15). If they exist, middle hooks are located on the posterior end of the disc, whereas the edge or marginal hooks, numbering six are lying on the anterior edge of the disc, and, further, singly in the center of each sucker, and the remaining four on the posterior edge between the first pair of suckers. 30 Sphyranuridae (the only genus Sphyranura, see page 401 ) is characterized by a disc which is transversely elongated and sharply de- lineated from the body on which there are two powerful suckers, two nniddle hooks and 16 edge hooks of which two are located in the suckers and the remaining along the edge of the disc. Hexabothrildae (Fig. 2) are characterized by the presence of a well-isolated disc, carrying on the posterior end a more or less well-developed appendage of signifi- cantly smaller diameter than the disc itself. Six powerfully developed suckers are located on the disc. Along the middle line a strongly curved long hook is located in such a way that its sharp edge is located near the inner surface of the sucker while its remaining portion is located in its interior (or within the tissue of the sucker, nobis ). Undoubtedly, in spite of this powerful development these hooks are homologous to the corresponding edge or mar- ginal hooks of the Polystomatidae and other families. The posterior appendage carries two well -developed suckers which are apparently devoid of hooks on its free lower edge. Between these appendage suckers there exists usually one pair of small middle hooks. In a number of species the middle liooks are absent alto- gether. One must indicate, nevertheless, that the question relative to the chitinous armature of Hexabothriidae demands reinves- tigation (see page 406). aiMM Fig. 48. Heterocotyle sp. , attaching disc of an adult individual from the gills of Dasybatus zugei M. H. from the region of Nagasaki (East China Sea). The family Diclybothriidae close to the preceeding one has an analogous disc, nevertheless six of its suckers, also equipped with power- fully developed chitinous hooks, stand much closer in their structure and function to the valves of the successive families than to the actual suckers. The absence of the chitinous parts characteristic of clamps draws them closer to the latter, but during the research on live subjects it is clearly seen that their common configuration and their method of attachment is of typically valve -type character. The posterior appendage is well developed in the genus Diclybothrium (Fig. 51) and is almost completely reduced in the second genus Paradiclybothrium (Fig. 52). When the posterior append- age is developed, it carries two rudimentary suckers and four pairs of hooks. Two pairs of hooks have the same shape or form as those in the suckers. One pair represents the unchanged small edge hooks and the latter represents small central or middle hooks. (For details see the chapter on embryology, page 101 . ) Among Paradiclybothriunri the chitinous p. 38 31 hooks (apparently all four pairs, although so far it has not been possible to detect a pair of the small edge hooks) are preserved together with a strongly reduced appendage, but both suckers (highly reduced to a great extent in the preceeding genus) completely disappear. Fig. 49. Leptocotyle minor (Monticelli), adult worm from the skin of the dorsal fin of the young Scyliorhinus canicula (L. ) from the Bay of Naples (Mediterranean Sea). Fig. 50. Neopolystoma palpe- brae Strelkow, adult worm from beneath the lower eyelid of Amyda sinensis (Weig. ) from Hanka Lake. The ensuing families (Chimaericolidae, Fig. 53; Mazocraeidae, Fig. 24; Hexostomatidae, Fig. 37; Discocotylidae , Fig. 2Z8; Anthocoty- lidae. Fig. 42; Plectanocotylidae , Fig. 88; Diclidophoridae , Fig. 54; Microcotylidae, Fig. 23; Gastrocotylidae, Fig. 7; Protomicrocotylidae, Fig. 89) are characterized by the presence of an attaching disc which is delineated fronn the body of the animal in varying degrees and bears, as a rule, a varying number of chitinous hooks which may be, however, absent in adult forms, and also bearing a varying number of attaching clamps. The number of chitinous hooks fluctuates from one to four pairs and the number of clamps fluctuates from one to several scores (above 100) of pairs. Four pairs of clamps and not more than three pairs of chitinous hooks are charac- 32 \^\ wfev 's^L J \oo? p. 39 /mm !^b' HlcH \oo bo\ 2 mm Fig. 51. Diclybothrium armatum Leuckart, Fig. 52. Paradiclybothrium pacificum Bychowsk/ and adult worm from the gills Gussew, adult worm from of Acipenser stellatus (Pall. ) from the Delta of the Volga (Accord- ing to Bychowsky and Gussew, 1950). the gills of Acipenser medirostris Agr. from the Tartar Straits (Sea of Japan). (According to Bychowsky and Gussew, 1950). Fig. 53. Chimaeri- cola leptogaster (Leuckart), adult worm from the gills of Chimaera mons- trosa L. from the Norvv'egian Sea near Sere Island. 33 teristic of the majority of the above-mentioned fanriilies .whereas among Gastrocotylidae and Microcotvlidae the number of clannps varies from six pairs upwards, whereas the ciiitinous hooks, for the most part, number four pairs or are absent in the adult. External Covers. External covers of monogenetic trematodes p. 40 are represented by a cuticle typical for the parasitic flatworms (Fig. 55), for the most part double-layered, smooth, and comparatively thin, under which is located a more or less well-developed basal membrane which, in a number of cases, is poorly visible. Because of this poor visibility, certain authors question its presence altogether. As a rule, subcuticular cells are absent in the nnonogenetic trematodes; if in rare cases they exist then they are in relatively small numbers and are under and partially between the fibers of the longitudinal, circular and diagonal muscle layers. As among other Cerco- meromorpha, the question of the covering of the monogenetic trema- todes is very complex and there is no commonly accepted opinion con- cerning its origin. The most wide- spread is that the cuticle represents a derivative of the ectodermal epithel- ium which, as a result of its adapta- tion to parasitism receded into the body and is represented by subcuti- cular cells or so-called submerged epithelium. This point of view is shared by many zoologists. The com- parison of the structure of the cover- ings in Cercomeromorpha and Tur- bellaria serves as a basis for this. Thus, in a series of Acoela and Triclada the receding of epithelial cells into the body under the dermal musculature is observed, that is, one observes the relationships which are close to those which are seen among parasitic flatworms. Analogous views can be seen among parasitic Myzostomidae (Fedotov, 1915). How- ever, other points of view exist. Thus, Monticelli, (Monticelli, 1893) sup- posed that the cuticula represents an ectoderm which underwent conaplete metamorphosis and which has a changed protoplasm, missing nuclei and missing delineations between the cells. This supposition is based on the Fig. 54. Dichlidophora denticulata (Olsson), adult worm from the gills of PoUachius virens (L. ) from the Barents Sea. 34 finding of circular, rbund, small bodies in the cuticular structure of the young worms. Finally, a number of researchers headed by Pratt (Pratt, 1909) and Schneider (Schneider, 1873) suppose that adult forms of para- sitic flatworms have lost their epithelium completely, which thus is pre- sent only among larval stages and is cast off during metamorphosis. ODtMM Fig. 55. Coverings of monogenetic trematodes. A- - Ancylodiscoides magnus Bychowsky and Nagibina; B - - Aca nthocotyle williamsi Price; C--Tristoma coccineum Cuvier. According to this point of view, the cuticle of parasitic flatwornns is a derivative of the parenchyma and is equivalent to the basal membrane of Turbellaria. This point of view was advanced in recent times by Poche (Poche, 1929) who proposed to replace the appellation "cuticle" for para- sitic flatworms by a new one "pseudodermis" and for subcuticular cells the appellation "pseudodermals" (pseudoderinal cells). p. 41 35 The opinion of Monticelli hardly corresponds to reality. The remaining two points of view have sufficiently weighty evidence to support them. For monogenetic trematodes we think it more probable that there is no covering epithelium in the adult form, although the first point of view, which is more commonly accepted, deserves more attention. The reasons according to which we are led to the opinion that there is an absence of epithelial cells in the adult forms of monogenetic trematodes are the follow- ing. First of all, a nnajority of authors who studied the coverings of mono- genetic trematodes did not discover any traces "of subcuticular cells. " p. 42 Thus, during the examination of over 100 species of marine Monogenoidea Goto, Cerfontaine and Maclaren (Maclaren, 1903) never found them once. Under more careful study, the cells of the receded epithelium of monogenetic trematodes, described by certain authors, appear not to be subcuticular epithelium but various types of glandular cells. Until now, no one has succeeded in presenting convincing views (drawings, nobis) of sub- merged epithelium among Monogenoidea. The data of I. V. Ivanov (1952) can be considered the only serious material on the subject. Ivanov found, after becoming acquainted with our slides of Acanthocotyle , that among this type, the covers as he writes, "possess all the characteristic peculiarities of the classical submerged epithelium. " However, it seems to us that this is not altogether accurate and that at any rate it demands more thorough study. During the study of the same slides one notices that the disposition of the "sub-cuticular" cells, which are clearly seen and which lie in their main aggregate under the dorsal surface of the body of the animal but which can also be seen as well on the ventral side, is not equal. Basically as is seen from Fig. 55-B, the "little stems" of the cells are not linked to the cuticle but to the muscular fibers located beneath it. In sections one can clearly see that the parenchyma directly joins the cuticle in the spaces between the cut muscular fibers, whereas, one does not observe "the little stems" of the "sub-cuticular cells" in these places. Thus, so far we hesitate to speak with certainty concerning the connection of these cells to the cuticle. Also, peculiarities of the embryology of monogenetic trematodes seem to us substantial when we see that the ciliated epithelium does not undergo metamorphosis at the attachment of free -swimming larva but peels off completely and falls away. This pertains not only to the species where the ciliated epithelium is arranged in special areas but also to the species where the entire body is more or less covered with ciliated epithelium. From what has been said above, it is understandable why it seems to us that the most probable supposition is that the cuticle of mono- genetic treinatodes appears to be a derivative of the parenchyma. The pre- sence of cuticular armature in a number of soecies can be considered as a 36 substantial objection to this supposition, but at the time of development of the animal, the basic chitinous elements of armament are formed, not directly in the cuticle but in the mass of the parenchyma. How to recognize all these significantly contradictory data without special research does not appear clear to us. 1 1 During recent years numerous data concerning the structure of the epith- elium of digenetic trematodes and tapeworms were published by Logachev (1953-1955). His works deserve more careful attention. Dermal glandular cells which, as was pointed out, are strongly developed in the main are grouped in the anterior and posterior ends of the body. Near the anterior end they are located mainly along the sides of the pharynx and along the buccal aperture, and open outside terminally or sub- terminally. Apparently the head glands of Monogenoidea are homologous to the head glands of the larvae of Gyrocotylidae, Cestodaria, Udonellidae, and also to the frontal glands of turbellarians. The glands of the anterior end of the body are most powerfully developed among Dactylogyrus but they are often also encountered among the remaining monogenetic trematodes, and among the latter they are relatively more strongly developed during p. 43 the early stages of the life cycle. The overwhelming majority of the dermal glands are of the sticky or glutinous type and to a lesser degree one also encounters the lachrymous type. The presence of poisonous (narcotic?, nobis) dermal glands, characteristic of a number of turbellaria, is pro- bable among monogenetic trematodes, however, we do not have exact data relative to this subject. Besides the dermal glands there are also glandular cells located in the main body of the parenchyma which are of uncertain origin. These are large cells lying for the most part in groups in the pos- terior end of the body and opening to the outside in the attaching disc. To this group are related,, for example, the powerful cells'of the so-called post seminal glands described in detail by Goto and Kikuchi (Goto and Kikuchi, 1917) for Dactylogyrus inversus Goto and Kikuchi, and widely distributed among Dactylogyridae. Excretory ducts of all the dermal glands open on the surface of the body of the animals by unarmed apertures. Armature of the cuticle occurs relatively rarely. Among Diplectanidae the cuticle is covered by delicate scales predominantly on the posterior half of the body and also partially on the attaching disc (Fig. 56). These little scales have a more or less sharpened front edge which extends freely above the surface, while the more rounded edge lies in the body of the cuticle. Besides that, Rhamnocercinae are armed by real thorns (see page 359). Among a number of Capsalidae there is strong cuticular armament consisting of a varying number of thorns lying mainly along the sides of the dorsal surface of the body. These thorns are located in parallel rows, each consisting of several thorns. The shape of the thorns 37 lf.OtMM Fig. 56. Diplectanum aculeatum varies (Fig. 57) from simply arranged needle-shaped thorns to complex thorns with numerous points on the free edge and with a massive basal part. In a number of cases, these thorns are equipped with special musculature and can move independently of each other. In separate species the number of rows of thorns fluctuates from a significant number (more than 100) to comparatively few (a little more than 10) while among the species with a smaller number of rows the shape of the thorns is usually the most complex. In addition to that, among species with a small number of rows of thorns, the edge of the body forms symmetrical growths, and the thorns are located in the middle of these growths. The complex of the growth with thorns, which is sup- plied with a special musculature, is very reminiscent of the para- podia of higher worms and un- doubtedly represents a primitive formation which aids in locomotion; we called it a propodium (Fig. 58). The question concerning these propodia and their development and morphology will be examined in detail in another work. The musculature is very strongly developed among monogenetic tre- matodes, particularly in the region of the attaching apparatus. It is rep- resented by dermal parenchymatose fibers (concerning the musculature of the sexual ducts and organs, see page 4 ). The dermal musculature typi- cally consists of circular, diagonal and longitudinal fibers. As a rule the longitudinal musculature is the most powerfully developed, often it forms powerful longitudinal muscular W1'2mm\ \ \ „ ^ \ y { \ ligatures (ligaments, nobis) which These Parona and Perugia, the posterior end of the body of an adult v/orm from the gills of Corvina nigra Cuv. and Val. from the region of Karadaga (Black Sea). Fig. 57. Skin thorns of various shapes, Capsalidae. are isolated from each other, ligatures which are mainly located on the posterior end of the body, change into muscles which serve for the move- ment of the central elements of the attaching armamert and for common coordinating movement of the entire attaching disc. According to Maclaren, in Diplectanum aequans Wagener (Fig. 59) the longitudinal dermal muscula- ture falls into two layers, exterior --lying directly under the circular layer, and interior--lying under the diagonal layer. Similar relationships have a certain similarity with the disposition of musculature of the dermomuscular sac among Gyrocotyloidea and Cestoidea. There are indications which point to the absence of the diagonal musculature among certain Hexabothriidae. 44 38 It is curious that among certain forms (for instance Diclybothriidae) one observes more powerful development of the dorsal musculature, whereas among the majority of monogenetic trematodes the musculature of the ventral side is the most powerfully developed. Parenchymatose muscular fibers are chiefly located in the main portion of the body in more or less well-developed dorso- ventral bunches. Less frequently, one encounters fibers which stretch longitudinally as in Cestoidea. Such disposition of the fibers is usually observed in the anterior or posterior ends of the body. Fig. 58. Capsaloides sp. , propodia of the adult worm from Tetrapturus sp. Parenchyma. Parenchyma fills the entire body between the dermal muscular sac and the in- ternal organs and has the appear- ance of polygonal cells, or more seldom syncytial tissues with numerous interior gaps between the cells which are filled with a from the region of Woods Hole (Atlantic colorless fluid. The latter is de- Ocean), void of formed elements. Often parenchyma has a fibrillar structure; sometimes it is differentiated, it is true to a small degree, into ecto- and endoparenchyma as occurs in Cestoidea. As Goto indicates, parenchyma divides very sharply into ectoparenchyma and endoparenchyma in Heteraxine heterocerca Goto. At the same time, he even notes the pre- sence of a special membrane which lies between these layers (Fig. 60). Digestive System. The digestive system for the most part is very strongly developed among monogenetic trematodes. It is represented by a pharyngeal apparatus, esophagus and intestine. 45 The buccal aperture is located subterminally and less often terminally. Around the buccal aperture one can sometimes observe lip like growths, more often, however, its edge is smooth. The buccal aperture usually leads into the buccal funnel which is often surrounded by a more or less isolated sucker, or on the interior edges of the funnel there can be, as has been mentioned above, two suckers developed in varying degrees. All these formations serve for the attachment of the anterior end of the worm's body during feeding. Posterior to the buccal funnel lies a more or less well-developed buccal Fig. 59. Diplectanum aequans Wagener, diagram of the cross section of the ventral coverings. (According to Maclaren 1903) 39 cavity which changes into a sac close to the pharynx or prepharynx. This prepharyngeal sac has the same structure as in Rhabdo- coela. Among a number of species the pharynx can protrude to the outside (the majority of the lower Monogenoidea), but among others it is devoid of this capability. •'>>^'.'?; Fig. 60. Heteraxine heterocerca (Goto), cross section of the body below the sex aperture. Enlarged 200 times. (According to Goto, 1894). Pharynx . The pharynx is usually the very powerful type of pharynx plicatus and pharynx bulbosus of the Turbellaria. Its form is round and somewhat elongated, in rare cases barrel-shaped, egg-shaped, etc. The pharynx is separated from the sac or parenchyma which surrounds it by a special membrane; this same type of membrane limits its interior lumen which often has a tetrahedral outline. The structure of the pharynx is complex and to a known degree resembles the structure of the suckers which can also be explained by a functional similarity (among certain Capsalidae the pharynx even functions in place of the anterior suckers). p. 46 Usually in the pharynx there is a strongly developed musculature which con- sists for the most part of three layers, external and internal circular layers and the middle radial layer (Fig. 61). Very often there are weakly developed longitudinal fibers. Often the number of the layers increases and the pharynx becomes much more complex. Between the muscular fibers are located the numerous nuclei belonging to the muscle cells and often mononuclear phary- ngeal glands are located in the main part of the pharynx. The latter can lie also in the adjacent parenchynr\a and only pierce the body of the pharynx by their canals. Very often very powerfully developed supplementary glands called salivary or postpharyngeal open into the lower end of the pharynx along with these glands (Fig. 62). Among certain Gyrodactylidae the pharynx is divided into two parts of which the first consists of several pyramidal cells and the posterior part is rounded, usually of muscular structure (Fig. 63). 40 The pyramidal cells of the interior part of the pharynx of the Gyrodactylidae possess great mobility and can powerfully extend and contract. Their function is not known, but apparently they have a certain relationship to the pulling off of the epithelial cells of the host during feeding. Among monogenetic trenna- todes the esophagus for the most part is short or may be completely absent. Among forms with relatively long esophagi it often forms lateral blind outgrowths which can branch strongly. In other cases, the esopha- gus has the appearance of a straight pipe and changes directly into the intestinal tract. Among many forms, the presence of a powerful muscular sphincter, the contraction of which interrupts the passage of food into and out of the tract at the beginning of the esophagus, is characteristic. Numerous monocellular glands, which are observed in certain Mono- cotylidae, can open into the esopha- gus. It is interesting that these glands are absent among the highest monogenetic trematodes, for instance among Microcotylidae and Hexabothriidae, Goto also calls these glands "salivary. " 0.1 HM Fig. 61. Nitzchia sturionis (Abild- gaard), cross section through the pharynx of the worm, from the buccal cavity of Huso huso (L. ) near the Island of Sara (Caspian Sea). Intestine. The intestine of monogenetic trematodes historically p. 47 evolved from the sac -like one of Rhabdocoela and during the individual on- togeny also iindergoes a similar stage (see the chapter on embryology) and is characterized by the absence of an anal opening. Usually the intestine has the appearance of two trunks stretching along the entire body, less often it is simple in the form of a more or less long pipe (Tetra- onchidae, Figs, 29, 64; Tetra- onchoididae. Figs, 29; and certain others). The two -branched intes- tine can be of varied shape. Intes- tinal trunks can be smooth in the shape of cylindrical pipes and end blindly (Gyrodactylidae, Fig. 12, a number of Ancyrocephalinae etc. ), or they can have a number of lateral growths and branches along their length and finally. Fig, 62, Polystonna integerrlmum Froelich, frontal section of the anterior part of the body. Salivary glands appear dark. 41 forming or not forming any branches, they may merge at the posterior end of the body, forming in this fashion a round or ellipsoidal figure (Dactylo- gyridae. Fig. 5). Very often when the ends of the intestinal trunks nnerge, a single smooth or branched extension stretches from the place of the junction posterior towards the attaching disc. The formation of lateral branches is observed both in forms with the trwo-trunked intestine as well as among the single-trunked, as for instance in Diplozoon para- doxum Nordmann(Fig. 231). We also note that the growths and branches of the intestinal trunks oriented inside the body can merge forming anastomoses between two trunks and givJng the intestines a OOImm] B.Imm Fig. 63. Gyrodactylus atherinae Bychowsky, anterior end of the body of an adult worm from the gills of Atherina mochan pontica caspia Eichw. near the Island of Sara (Caspian Sea). Strongly flattened (semi-diagrammatic). Fig. 64. Tetraonchus monenteron (Wagener), adult worm from the gills of Esox lucius L. from the Delta of the Volga. Vitelline follicles at the posterior end of the body are somewhat rarified. strongly -branched form ( Polystoma , Fig. 22). Often the development of p these anastomoses is so powerful that the basic trunks become indistinguish- able (for instance among certain Microcotylidae, Fig. 66). Basically, smaller worms have a simpler form of intestine. The latter reaches the greatest complexity among the larger marine forms. One must note that complication of the intestine is observed independently in various syste- matic groups and is correlated with an increase in the size of the animal. Undoubtedly, a more equitable distribution of the food substances which are 48 42 absorbed by the walls of the intestine among the parts of the body of the animal is attained by this means. The structure of the intestinal wall, as the researches of Goto show, can be of two types. The first type is characteristic of Microcotylidae, Mazocraeidae, Diclidophoridae, and Hexabothriidae , and is distinguished by the fact that there is no continuous Fig. 65. Anclyodiscoides siluri (Zandt), adult worm from the gills of Silurus glanis L. from the Delta of the Volga. Fig. 66. Microcotyle reticulata Goto, adult worm. Natural size 6- 10 mm (According to Goto, 1894). epithelium in the intestinal wall but instead isolated large epithelial cells with numerous pigmented granules are situated upon the tunica propria (Fig. 67). The second type peculiar, according to Goto, to Gyrodactylidae Dactylogyridae, Monocotylidae and Capsalidae, is represented more or less by a typical cuboidal or columnar epithelium sometimes arranged in several layers (Fig. 68). For the forms of the first type, the absence of salivary glands of the esophagus is characteristic; for the second, their presence. Apparently, both types of digestive tracts are linked with differ- ent means of digestion. For the first type, digestion probably occurs in- side the intestinal canal, in the second type --intracellular, by way of active seizure of food particles which are prepared by the "salivary" glands. The picture of the intracellular digestion can be well observed in a number of forms, particularly among Polystomum integerrimum Froelich (Fig. 69). As a matter of fact, this question demands further special investigation. p. 49 43 Excretory System . The excretory system has been studied comparatively poorly. As opposed to the system of digenetic trerratodes, among Monogenoidea it apparently does not have systematic significance. In essence, the excretory system is composed of three parts: Protonephridia and their capillaries and system of ducts including basic trunks and end parts, which connect the excretory system with the outside. The proto- nephridia of monogenetic trematodes are in the shape of the usual end cells with ciliary flame. The capillaries leading from them resemble thin-walled pipes, often bearing on their walls ciliated epithelium as among the Turbellaria. Apparently these capillaries are intracellular formations. The number and disposition of these flame cells have been studied very in- sufficiently. The number of terminal protonephridial cells varies among O.Ihm Fig. 67. Squalonchocotyle spinacis (Goto), cross section through the intestinal branch. Enlarged 204 tinnes. (According to Goto, 1894). Fig. 68. Nitzschia sturionis (Abild- gaard), cross section through the intestinal branch. Worm from the gills of Huso huso (L. ). the adult forms (among the young ones see chapter on embryology). Thus in the anterior end of Diplectanum the number of flame cells, according to our observations, is not less than six on each side (Fig. 70). The capil- laries of protonephridia empty into canals which successively increase in size and merge together to form two main ones which are loacted along the sides of the body. The main canals stretch from the anterior end to the posterior end and sometimes reach into the attaching disc and return to the anterior end, often intertwining with its first half. The relationships between both halves can be very complex. Among the nnajority of Dactylo- gyridae, Monocotylidae, Capsalidae, and Polystomatidae and basal trunks in the anterior part of the body at the level of and somewhat higher than the pharynx form a rather complicated wavy part and join by cross commissures so that its excretory system is no longer separated into right and left inde- pendent parts but becomes unified (Fig. 71). Apparently among a number of forms there are similar connections also at the posterior end of the body, as for instance in Monocotyle ijimae Goto (Fig. 72). Among Calceostomella inermis, Parona and Perugia, basic ducts are faintly noticeable because p. 50 44 the entire excretory apparatus acquires a netlike character where a large part of the small as well as the large canals are equipped with a powerfully developed ciliated cover. Among a majority of forms the excretory system is colorless but among representatives of the genus Calceostoma the walls of the vessels and their liquid contents are often darkly tinted. 0.1mm Fig. 69. Polystoma integerrimum Froelich, sagittal section through the intestinal branch. The remnants of the frog's red blood corpuscles in the process of being digested appear in black in the cells of the intestinal epithelium. Fig. 70. Diplectanum aculeatum Parona and Perugia, excretory system of the anterior end of the body of an adult worm from the gills of Corvina nigra Cuv. and Val. from the region Karadaga (Black Sea). (Semi -diag rammatically ) . The terminal parts of the excretory system are located at the level of the pharynx or somewhat lower. They consist, on each side of the body, of a single canal which often forms, at some place along its length, a more or less well-developed contractile bladder--excretory bladder equipped with special musculature. The excretory vesicles or bladders open to the outside by independent apertures which are located either laterally or more often dorsolaterally. The snnall duct which is usually present between the excretory aperture and the bladder is equipped with a powerful muscular sphincter. Excretory vesicles are well-developed among many monogenetic trematodes but weakly noticeable among Mazo- craeidae, Microcotylidae, and families related to them. 45 Nervous System. The nervous system is relatively strongly developed and in some respects it is simplified in comparison with the turbellaria and in other respects it is significantly more complicated. The p. 51 cephalic brain among more primitive forms is located dorsally in front of the pharynx (Dactylogyridae, Tetraonchidae and others), and among more highly developed types, above the pharynx itself (Polystomatidae) or directly posterior to it (Microcotylidae and others). For the nnost part, the brain consists of two powerful ganglia joined by a single dorsal commissure (Figs. 73, 74). Among certain forms, head ganglia are joined by means of the dorsal and ventral commissures thus forming a nerve ring around the esophagus (Capsala, Nitzschia and others). Three to four pairs of anterior nerves emerge from the head ganglia, sometimes immediately separating into individual fibrillae and innervating the anterior end of the worm. As a rule, three pairs of nerve trunks ennerge behind the head ganglia: dorsal, Fig. 71. Polystoma integerrimum Froelich, head end of an adult worm showing the excretory system (junction of the right and left halves of the ducts in the anterior part of the body). (According to Zeller, 1872, simplified). Fig. 72. Monocotyle ijimae Goto, structure of the excietory system (the junction of the right and left halves of the ducts ! in the posterior part of the body). (According to Goto, 1894). lateral, and ventral. As a rule, the ventral pair is the most powerful and often forms a special ring of attaching disc on which are sometimes located the gangliose widenings corresponding to the attaching organs. Among the forms with asymmetrical attaching apparatuses, the ventral nerve trunks are also usually asymmetrical (Fig. 75). Among a number of forms the dorsal pair of nerve trunks is weakly developed and among some of them is 46 completely absent (as for instance anmong certain Diclidophoridae). The lateral pair of nerves always exists but is usually thinner and shorter than the ventral. Between the trunks comnmissures can be seen as was noted by Lang (Lang, 1880) for Capsala martinieri Bosc ( = Tristomum molae^ auct . ) (Fig. 76). The nerves which lead from the main nerve trunks usually divide into a network of nerves which interlace the entire periphery of the animal. When the nervous system of monogenetic trematodes and Rhabdocoela are compared, a complete coincidence of main traits is evident (aside from the secondary traits which are connected with the powerful development of the attaching organs among monogenetic trematodes). p. 52 Fig. 73. Polystoma integerrimum Froelich, diagram of tVe anterior part of the nervous system of an adult worm, dorsal view, (Accord- ing to Andre, 1910). Fig. 74. Polystoma integerrimum P3\j;,elich, the same diagram, lateral view. (According to Andre, 1910). Especially interesting are two aspects --immediate separation of the a^iterior nei*ves into separate fibrillae, and the weak development of the commissures between the main nerve trunks within the limits of both groups. Organs of feeling are represented by eyes and sensitive nerve endings scattered within the cuticle along the entire body, but which occur in greater numbers close to the anterior edge and near the attaching organs. The sensitive fibrillae described by a number of authors apparently do not exist. It has not yet been ascertained if the special suckers located on the dorsal side of a number of Capsalidae have any relation to the organs of feeling. 47 The eyes of monogenetic trematodes are mostly paired in two pairs or more seldom, one pair. Annong the highest Monogenoidea one finds only one eye but of the paired type by its origin. The indication of the presence of six to eight eye spots in (Hexabothrium appendiculatum Kuehn) was erroneous as we have explained before. What was mistaken for eyes proved to be glandular cells. The eyes are located on the dorsal side of the body usually above the pharynx or in front of it closer to the anterior end. For the most part, eyes are of different sizes --the anterior Fig. 75. Heteraxine heterocerca (Goto), nervous system of the adult worm. (According to Goto, 1894, simplified). Fig. 76. Capsala martinieri Bosc, nervous system of the adult worm. Somewhat diagramnnatized and and simplified. (According to Lang, 1880). pair is usually smaller than the posterior, however, the reverse relation- ship is also observed. Often the eyes are strongly reduced or even com- pletely disappear. The reduction and degeneration of the eyes can be easily traced in a number of Dactylogyridae especially among representatives of the genus Acolpenteron which are parasites of the ureters of their hosts. A number of fornas have eyes only in the early stages of development. The structure of the eyes is prinaitive enough (Fig. 77). Usually the eye is in- verted and consists of a pigmented globule in the shape of one large cell varying in color from amber to black and consisting mostly of unicellular retinae with a fringe of rods adjoining directly the pigmented globule from its concave side or adjoining a special layer lying between the retinae and the pigmented globule. These rods are usually analogous to the eye rods of higher animals. Among a nunriber of forms there is also a special light refracting little-lens which lies in front of the eye globule. Andre's 53 48 assertion (Andre, 1910b) of the absence of these lenses among Polystoma integerrimum Froelich is erroneous and is based on a study of small numbers of young individuals; the presence of lenses in a number of mono- genetic trematodes was verified by us not only on live subjects but also on slides stained with the usual histological colors. Among forms having a single eye, the eye is usually equipped with two lenses which enables us, during the study of live subjects, to suggest that such an eye is a result of the fusion or nnerging of the two eyes first existing in phylogenesis. Eye- nerves are usually very short and emerge from the dorsal side of the anterior part of the head ganglia. As Goto accurately points out, among adult monogenetic trematodes the eyes are in the process of disappearing and apparently do not function. Fig. 77. Polystoma integerrimum Forelich, two eyes from one side of the body, semi-diagrammatic. Enlarged about 1300 times (According to Andre, 1910). From all of our observations, it is clear that the growth of the eyes occurs only during the tinne of the development of larvae in the egg; once it emerges from the egg its eyes grow no more and in many forms the p. 54 eyes are subjected to reduction or even complete disappearance during onto- genesis. Sex System. All monogenetic trematodes without exception are hermaphrodites. They usually have one common sex pore ( porus genitalis Qorrmvunis ) , leading into the sex atrium into which opens the seminal ejacu- latory canal or the male copulative organ and finally the uterus; rarely there are separate openings of the male and female sex systems; sometimes the seminal ejaculatory duct opens into the terminal part of the uterus. Usually the common sex opening is located nnore or less medially on the ventral side of the body, posterior to the esophagus or posterior to the bifurcation of the intestinal trunk; more rarely it is located slightly to the side in front of or behind the intestinal trunks, or it can be displaced completely laterally. In addition to the common sex pore, among a majority of forms there exist 49 one to two vaginal openings which are located in different positions either on the ventral side or along the sides, or on the dorsal side of the body and may be located both at the level of the ovary and closer to the anterior end or, on the contrary, to the posterior end of the body. Thus, among mono- genetic trematodes the number of external pores of the sex system fluctu- ates from one to four. In addition to that, among many forms, predominantly the more highly organized ones, there is a special duct of the sex system which connects it to the digestive system (see pageVl ). The sex atrium, (atrium genital e communae) (Fig. 78) is pre- sent among a number of monogenetic trematodes and in the simplest cases represents a small cavity separated from the external medium by a narrow 03mm Fig. 78. Microcotyle sebastis G oto, sagittal section through the body of the worm in the region of the sex atrium. Enlarged 245 times (According to Goto, 1894). Fig. 79. Parancyrocephalus daicoci Yamaguti, adult worm. (According to Yannaguti, 1938). part and resulting from a drawing -in of the exterior cuticle and often equipped with special musculature. Into this sex atrium the uterus opens more ventrally, and the male sex system also opens somewhat closer to the dorsal surface. Along with such simple structure of the atrium con- siderable complications occur. Often the common atrium forms two more or less well-developed concavities into which sex ducts open. The common 50 cavity can remain sufficiently large or be considerably reduced in size. These concavities, which were formed in a secondary fashion, can be con- sidered as male or female atria (^atrium masculinum and atrium feminiurn). Independently from the isolation of the divided atria, a chitinous armature in the shape of varying forms of hooks analogous and perhaps even homol- ogous to those of the male copulatory apparatus is formed on the upper in- terior surface of the common sex atrium among many more highly organized p. 55 types, especially among Microcotylidae. These hooks, which are charac- teristic for the separate species, can be located directly on the upper wall of the atrium or in the special concavity or even in a special muscular sex papilla separated by a special membrane from the surrounding tissues but not connected with the terminal part of the male sex ducts. The male sex system among monogenetic trematodes is repre- sented by well -developed seminal ducts, seminal reservoirs, supplementary glands, and a copulatory apparatus. The male gonads for the most part are in the shape of rounded bodies, more rarely they are lobulated or of some other form. The number of testes varies but the basic number is one. The opinion of Fuhr- mann that the two testes appear to be primary is completely faulty and is based on an analogy with digenetic trematodes. Within limits of the sepa- rate groups the number of testes is smaller among the most primitive forms than among the highly organized ones. Thus among Dactylogyrus and, close to it, Ancyrocephalus and others, the number of testes always equals one. In the species Parancyrocephaloides daicoci Yamaguti, a form which is close to the ones mentioned above, there is also one testis but it is bifur- cated from the posterior end almost to the anterior edge (Fig. 79). The p. 56 fact that we deal here with the beginning of the bifurcation of the testis and not with the reverse process is substantiated by the presence of a single seminal duct emanating from the anterior end of the testis. Finally, among the more highly organized form Linguadactyla molvae Brinkmann, related to the same group, the number of gonads is considerable (Fig. 21). With- in the limits of the aberrent group, Microbothriidae, there is one testis among Leptobothrium and Leptocotyle , there are two lying symmetrically side by side among Dermophthirius and finally, many in the shape of follicles closely pressed to each other among Microbothrium . Among Mono- cotylidae there is a number of genera having from one to a multitude of testes. Among representatives of Heterocotyle and Dasybatotrema there is only one testis (Fig, 80), Empruthotrema raiae MacCallum has a testis bifurcated from the anterior end almost to the posterior end or, to be more precise, folded in two because the seminal duct emerges from one of the anterior ends (Fig. 15). Among the species of the genus Dionchus there are two testes lying one behind the other (Fig. 16), and among Monocotyle -- three, of which one lies behind and two symmetrically side by side and p. 57 closely contiguous in front of the rear one (Fig. 27). Finally among many genera, as for instance Calicotyle there are nunnerous testes (Fig, 81), 51 |L Among Polystomatidae the increase in the number of testes frona one (genus Polystonnoides and others, Fig. 82) through two (Diplorchis, Fig. 83) to 25 and nnore ( Sphyranura , Fig. 35) is distinctly visible. The greatest number of testes occurs in Microcotylidae where it can be in excess of 200 annong separate representatives. However, in the odd genus Mazocraeoides there is only one testis (Fig. 84). The process of 0.1mm 1mm Fig. 80, A- -Heterocotyle sp. , adult worm from the gills of Dasybatus zugei M. H. from the region of Nagasaki (East China Sea), (original); B--Dasybatotrema dasybatis (MacCallum), adult worm. (According to Price, 1938). increase of the number of testes undoubtedly takes place independently in the different groups. In the majority of cases this increase is realized by the way of resulting division of the primary testis, mainly in a transverse direction to the testis and only after that in a longitudinal direction. Thus, this process takes place in all elongated forms. The increase of the number of testes from the beginning by the longitudinal subdivision occurs more rarely, mainly among types with considerable width. In certain cases the testes represent a follicular mass located closer to the ventral side of the body, a nnass about which it is difficult to say whether it represents a single or multiple organ (Fig. 85). Among the 52 p. 58 Fig. 83. Diplorchis ranae Fig. 84. Mazocraeoides dorosomatis Ozaki adult worm. Enlarged Yamaguti), adult worm from the gills of 16 times. (According to Clupandon punctatus Sohl. from the region Ozaki, 1935). of Kagoshima (East China Sea). Fig. 85. Polystoma integerrimum Froelich, sagittal section through the body in the region of the testes. 53 well-kno\vn Polystoma integerrimum Froelich the transition from a single rounded testis to such a foUicularly-merged one takes place during the on- togeny by way of the considerable growth and individualization of separate parts. p. 59 Fig. 81. Calicotyle kroyeri Diesing, Fig. 82. Polystomoides ocellatus adult worm from ^he skin rear the anal (Rudolphi), adult worm from the opening of Raja batis L. n'.ar the anterior part of the esophagus of southern shores of England (Atlantic Emys orbicularis (L. ) from the Ocean). Four eyes are visible on neighborhood of Poltava, the buccal sucker. Usually the testes are located in the po^Lerior half of the body behind the ovary but there are types ii which the-' lie mainly in the anterior part even though some may partially extend beyor d the ovary. Among Cyclobothrium sessilis (Goto) numerous testes are located in the proximity of the sex pore. Their number is more or less the same both in front of the ovary and behind it (Fig. 86). Among Diclidophora pollachii (Beneden and Hesse) the testes are located generally in the same way as in the preceeding species, but the number of testes lying closer to the anterior part is almost twice as large as those lying behind the ovary (Fig. 87). Annong Octoplectanocotyle trichiuri Yannaguti, the number of testes 'yi'^g in front of the ovary is also larger than those lying behind (Fig. 88). Finally, among Protomicrocotyle pacifica Meserve, all the numerous l, tes lie in front of the ovary (Fig. 89). The distribution of the testes in the depth of the body varies: they either lie in the middle between the ventral and dorsal surface, or closer to the ventral side. In separate cases, the testes 60 54 are arranged into two layers, Diclybothrium armatum Leuckart (Fig. 90). The testes are well- delineated from the surrounding parenchyma by a special connective tissue membrane. Sperm of monogenetic trematodes arc usually thread-like and relatively long. Fig. 86. Cyclobothrium sessilis (Goto), adult worm. (According to Goto, 1894). Fig. 87. Diclidophora poUachi (Beneden and Hesse), adult worm. (According to Braun, 1889-1893, somewhat simplified). Seminal ducts are represented by efferent ducts (vasa efferentia) and by a seminal duct (vas deferens), canals The comparatively short little efferent which unite in pairs and then merge into one more or less long seminal duct emanate from the testes. Goto (Goto 1894) indicated, however, that among the highest Monogenoidea he did not see any efferent ducts and supposes that the sperm pass from one testis to another by a system of lacunae of parenchymatous origin. Among the species with a single testis, the duct which emerges from it is designated as a seminal duct. It is usually more or less powerfully twisted (serpentine, and often coiled as well, nobis ) and starts from the testis at the ventral side of the body or in the middle of its thickness and quickly rising to its dorsal surface, goes to the anterior end of the body p. 61 55 and descends to the ventral side only in the vicinity of the sex pore. As a rule the senninal duct is single, however, in Paradiclybothrium pacificum, described by us and A. V. Gussew there are two of them (Bychowsky and Gussew, 1950). From the testis, starting at first along the ventral and then closer to the dorsal side, emerge two ducts lying along the sides of the body parallel to the intestinal trunks, now closer to the middle, now directly over them, and in front they merge into one. The reasons for the formation of two seminal ducts instead of one are not clear; however, there is no doubt that this phenomenon is secondary and quite possibly connected nsuM Fig. 88. Octoplectanocotyle trichiuri Fig. 89. Protomicrocotyle pacifica Yamaguti, adult worm (According to Meserve. (Combined from two Yamaguti, 1937). drawings of Meserve, 1938). with the very powerful development of the uterus which, so to speak, divides the middle part of the duct. The histological structure of the seminal ducts has been poorly studied. They are sharply delineated from the parenchyma by a special membrane toward the inside of which is located the epithelial layer with a few rounded nuclei. Apparently, at least in a number of types, there also exists a circular musculature independently under the membrane. This can be observed in Polystoma integerrimum Froelich (Fig. 91) and in a number of other forms, fresh water as well as marine. 56 The seminal duct passes at its terminal part into the seminal ejaculatory canal (ductus ejaculatorius) forming, for the most part, either one or several widenings of varying shape and location in front of the latter, which appear as reservoirs for the full, ripe sperm (vesicula seminalis externa). HtNM Fig. 90. Diclybothrium armatum Leuckart, cross section of the body in the region of the testes. As a rule this ductus ejaculatorus is supplied with a sufficiently powerful musculature, it is of insignificant length and opens into the sex atrium on its terminal part, or its terminal part enters into the differently arranged copulatory organ, or finally it changes into a chitinous pipe which represents its direct continuation. In most cases a number oi monocellular or poly- cellular glands of different origin opens in- to the ductus ejaculatorius. These glands are of two types, prostate and granule -con- taining. More often they are more power- fully developed among the forms with chiti- nous sex armature and weaker among those that have muscular copulatory organs. Pro- state and granule-forming glands very often especially among Dactylogyridae and types close to them, form ampule-shaped reser- voirs lying in direct proximity to the sex pore (Fig. 92). The physiological signifi- cance of these formations has not been elucidated so far. p. 62 0.1mm Fig. 91. Polystoma integer- rimum Froelich, frontal section through the seminal duct ( vas d eferens ). The copulatory organ of mono- genetic trematodes has a very diversified jtructure. Basically, one can consider two types of structures characteristic for them: in the shape of the muscular penis protruding through the sex pore, or in the shape of a completely chitinous formation. The main peculiarity in M .no- genoidea is the absence among them of the turning inside out, (eversil le, nobis ) muscular sac enclosed in a special cirrus which is so characte ^-istic and Trematoda. for Cestoldea All indications of the presence of cir: > among 57 monogenetic trematodes are faulty and appear as a result of inattentive study of the copulatory organs of Capsalidae in which the penis really re- sembles a cirrus but nevertheless, as will be seen later on, is fashioned along the type common for Monogenoidea (see however, page 476 ). Gener- ally the corresponding schemes of structures of copulatory organs of Rhabdocoela can be applied wholly also to such monogenetic trematodes. a02n Fig. 92. Anclyodiscoides magnus Bychowsky and Nagibina, cross section in the region of the prostate glands. In a more simple (from a morphological point of view) case the ductus ejaculatorius , representing a slightly more muscular direct ex- tension of the seminal duct, opens directly into the sex atrium; at the same time, the role of the copulatory organ can be played by various formations not connected with these ducts and related to the sex atrium as has been indicated above. Thus, for instance, similar relations are characteristic for a number of Microcotylidae. Generally in isolated cases the sperm which falls into the sex atrium is ejected by its contraction without any special copulatory contrivances. A small muscular sucker at the end of the seminal ejaculatory canal (ductus ejaculatorius) appears as the most primitive but already isolated copulatory organ, (for instance among Microcotyle caudata p. 63 Goto, Fig. 93). This sucker is separated from the surrounding tissues by a special fold and can be extended into the sex atrium and beyond its limits through the sex pore. Morphologically it is little delineated from the sur- rounding tissue but has a more powerfully developed musculature, circular as well as longitudinal, further we can observe more and more the growth of the penis and also its giadual delineation from the surrounding tissues. All in ill in the most complicated case (Benedenia, Fig. 196) the penis is completely separated by a special membrane, its upper part really lies in a spherical pocket emanating from the sex atrium and the lower part is usually spherical and inflated--or flask-shaped, in the thickness of the parenchynna. The internal structure of such a penis is sufficiently complex. The ductus eiaculatorius which passes through its center usually forms a more or less well-developed interior seminal vesicle (vesicula seminalls 58 interna), sometimes divided into two or three separate chambers. The ducts of the prostate and granule -forming glands enter into the body of the posterior part of the penis and sometimes they form therein reservoirs where their secretions accun^ulate (vesicula prostatica interna and vesicula granulorum interna). On the upper free end of the penis very often are Fig. 93. Microcotyle caudata Goto, sagittal section of the body in the region of the sex aperture. In addition to the little sex sucker there is also an armed sex atrium. En- larged 250 times. (According to Goto, 1894). Fig. 94. Monocotyle ijimae Goto, sagittal section of the region of the sex aperture. Enlarged 140 times. (According to Goto, 1894). located, in different fashion but for the most part as a corona of more or less complicated configuration, chitinous thorns or hooks which as a rule are of sharply prescribed form and of constant number in each species. Among many types as was mentioned before, the terminal part of the sem- inal ejaculatory duct forms a chitinous pipe which either terminates at the end of the penis or even extends be- yond. In isolated cases (among cer- tain genera) the chitinous pipe is longer than the copulatory organ and extends not only forward from it but posteriorly; very often a special muscular formation, not correlated with the penis, is located on it--bulbus eiaculatorius (as for instance Monocotyle, Fig. 94). The histological structure of the penis can become very complicated. Its muscu- lature is usually arranged in four layers, an exterior circular--adjacent to the surrounding membrane, two p. 64 Fig. 95. Capsala sp., cross section through the copulatory organ. 59 longitudinal and an interior circular, lying near the ejaculatory canal (Fig. 95); the space between the musculature, the outside of the exterior membrane and the epithelium of the canal is filled by cells of the connecting tissue. The second type of copulatory organ among monogenetic trema- todes is represented entirely by a chitinous formation lying in a special envelope, and provided with separate muscular retractors (for instance, Dactylogyridae, Fig. 9S). Without doubt, this type of copulatory organ Fig. 96. Chitinous copulatory organs of different shapes, Dactylogyrus spp. Drawn at different magnifications. originates from the chitinous armature of the pear-shaped organs of the free living flatworms as is the case among Turbellaria (Beklemeschev, 1937). The ejaculatory duct among corresponding forms is practically re- placed by a special chitinous pipe into the base of which enters the ejacula- tory duct and the glandular ducts --prostate and granule -forming. The for- mation of the pipe is mostly widened and the ejaculatory duct forms a widen- ing seminal vesicle in its cavity. The pipe itself is of varying shape and length. Annong some forms it is almost straight and broad, in others it is thin, sometimes very long, curved, and twisted completely or partially as a spiral, etc. In certain cases the diameter of this pipe, which plays — generally speaking, the role of the penis, changes along its extension very significantly, now narrowing itself toward the free end, now widening. Usually in addition to the pipe there is a special chitinous complex support- ing it which is sometimes very intricately formed. The structure of the supporting apparatus and the pipe itself has a great significance in the 65 60 systematics of a number of groups of monogenetic trematodes .appearing as a good representative diagnostic sign. For various groups of monogenetic trematodes the presence of a particular type of copulatory organ is charac- teristic. Thus the lower Monogenoidea- -Protogyrodactylidae , Dactylogyridae, Tetraonchidae , Diplectanidae , Amphibdellatidae and others have a chitinous copulatory organ, Monocotylidae--a muscular penis usually weakly developed but often equipped with a chitinous pipe; Capsalidae and groups close to them have an unarmed penis, usually very powerful. Among Gyrodactylidae, Polystomatidae , and Sphyranuridae , a small sucker— type copulatory organ with a corona of chitinous hooks is characteristic. Among the highest Monogenoidea (Mazocraeidae , Microcotylidae and others) the penis for the most part is weakly developed, but on the other hand the chitinous hooks in the sex atrium are powerfully developed. The only genus which has no copulatory organ at all is Diplozoon, among representatives of which the terminal part of the seminal duct of one individual grows together with the ducts of the female sex system of the other. The fenaale sex system is of variable structure, differing even within the limits of a single systematic group. Basically it is represented among monogenetic trematodes by two large glands --ovary and vitelline, supplementary glands, and a nunnber of ducts serving for the egression or excretion of the glands, for the preservation and for the reception of sperm and the preservation and egression of the eggs. As a rule all monogenetic trematodes are oviparous with the exception of one viviparous fannily - Gyrodactylidae. The anatomy of the female sex system of the latter is much altered in connection with the live -bearing habit and will be succintly characterized separately at the end of the description of the female sex system. The ovary among monogenetic trenaatodes occurs singly and has varying shapes and sizes and in a majority of cases is located in the anterior part of the body in front of the male sex glands. In rare cases the ovary is displaced to the posterior half of the body and as an exception (for instance Vallisia and others) it is located behind the testes. The form of the ovary among fresh water Monogenoidea is for the nnost part rounded (Fig. 97A), and more seldom elongated (Fig, 97B), with a flask-shaped posterior part; whereas among the marine species the second form of ovary is the most common. Often the ovaries are strongly lengthened and significantly curved in the anterior part and in the posterior part they form not a flask shape, but a palmate shape (Fig. 97B). In certain cases the ovary is divided by a constriction into more or less equal parts. The flask type part of the elon- gated or the corresponding part of the round ovaries corresponds to the oogonial chamber and contains the early stages of the developing egg cells. The envelope of the ovary is of cellular structure and consists of flat, spindle- shaped cells; in the period which follows the laying of the eggs the cells of this envelope can strongly increase in size and possess the ability of seizing and digesting the unused egg cells (see page 84). p. 66 61 An oviduct emerges from the ovary on the side opposite to the oogonial chanaber. The latter is well isolated from the ovary, has a different structure than the envelope of the ovary, reaches a different length and ends entering the ootype. Fig. 97. Schematic representation of different types of ovaries of mono- genetic trematodes. Explanation in text. Among many Capsalidae and related forms a special chamber from which the oviduct emerges (Fig. 98) is isolated inside the ovary. This chamber apparently serves for the accumulation of a certain number of ripened egg cells before the beginning of accelerated egg laying. There is reason to believe that at the same time it can also serve as a receptaculum seminis inside the ovary. A number of ducts open into the oviduct in front of the ootype, to be specific, vitelline ducts, vaginal duct, and genito-intestinal duct. In addition to that receptaculum seminis O.Imh Fig. 98. Benedenia derzhavini (Layman), ovary with the in- terior chamber. also opens into the oviduct, or the ovi- duct itself forms a widening which is also designated as a receptaculum seminis . The places of junction of all of the enunne rated ducts into the oviduct can be very close together and then is fornned a comnnon large cavity in the oviduct which does not have a special name, but which plays a significant role in the functioning of the female sex system, as our study has shown, (see page 85 ). How- ever, it is more fitting to consider the oviduct as being divided into two separate parts. Specifically, as the oviduct (oviductus) must be considered that part which extends fronn the ovary to the place ot junction with the vitelline ducts, whereas the part leading from the vitelline duct to the 62 ootype must be designated as the female sex duct (ductus communis). Such a division is much more satisfactory because of the fact that it can also be applied to Rhabdocoela. In passing, we would also like to indicate that among various groups the number of ducts entering the oviduct varies: often the vaginal and genito-intestinal ducts or one of them can be absent. p. 67 The vitelline ducts represent the most powerfully developed part of the female sex system. These are the follicular glands; as a rule there are two , less often one or three. They are usually powerfully developed and occupy almost the entire body starting from the head end and extending to the attaching disc, and often even extending into it; the vitellaria are located be- tween the intestines, the sex glands and the ducts and alnnost completely dis- place the parenchyma of the body. When the vitellaria are very strongly developed, they unite along the median line of the body in such a way that they have the shape of a single organ. However, even in these cases the double origin of the vitellaria is easy to establish by the presence of two efferent vitelline ducts. The latter emerge from each vitellar- ium one by one starting on the sides of the body; they extend mostly along the ventral side or more or less close to the medial line of the body and unite into a common vitelline duct which opens into the oviduct. Very often this unpaired or common vitelline canal forms a widening --a vitelline reservoir along its extension. The latter, however, for the most part does not reach significant dimensions. The vitellaria are arranged in similar fashion in all monogenetic trematodes with a few exceptions. Thus, among Diplozoon, there is only one vitelline gland and correspondingly one vitelline duct (Fig. 231) because of the peculiar Structure of its sex system connected with the presence of two worms grown together in its adult stage. This phenomenon is secondary. In the odd genus Trivitellina (Protogyrodactylidae) the vitellaria are divided into three groups of which each has its own independent vitelline duct, which then unites into a common one (Fig. 99, see however, page 360). Fig. 99. Trivitellina subrotunda Johnston and Tiegs, adult worm. Natural size about 0. 2 mm. (According to Johnston and Teigs, 1922). 63 The histological structure of the vitellaria is not of special in- terest. We shall note that each vitelline follicle is delineated from the parenchyma by a special nnembrane and contains usually a small number of vitelline cells. As regards the vitelline ducts, they usually have ciliated epithelia and are equipped with a well -developed musculature which is represented predominantly by circular fibers (Fig. 100). Both help in the rapid transfer of the vitelline cells to the oviduct. ■.©C£) 0.1mm Fig. 100. Polystoma integerrimum Froelich, sagittal section through the vitelline duct. h .^==^:^ C Fig. 101. Diagram of the location of the vaginal ducts among different genera of monogenetic trematodes: A--Dactylogyrus ; B --Tetrancistrum; C--Murraytrema; D- -Calicotyle, Merizcotyle; E- -Pseudocotyle ; F--Tristoma; Capsala; G--Polystoma; H- -Sphyranura; I--Rajonchocotyle; J--Chimaericola; (According to Brinkman, 1952) K- -Diclidophoropsis; Li- -Heteronchocotyle , Squalonchocotyle. (After Brinkmann, 195Z). 64 The vaginal duct can be present or absent. In a naajority of cases it is a single duct starting from the oviduct, however, among many forms we can observe two vaginal ducts emerging, not from the oviduct, but from the vitelline ducts. p. 68 The apertures of the vaginal ducts are variously located among the different species (Fig. 101). Thus among Dactylogyridae , Tetraonchidae and other lower monogenetic trematodes, if this duct exists, it is always single and its opening lies either on the dorsal or ventral side or, most p. frequently, more or less laterally. Among the types studied by A, V. Gussew "Dactylogyridae of the Hanka Lake" there is one species Dactylogyrus obscurus Gussew, among which one can suppose the presence of two vaginae; if this is so, then the secondary origin of this species is certain. 69 Fig. 102. Benedenia derzhavini (Layman), left edge of the anterior end of the body showing the common opening of the copula - tory organ, uterus and vagina. Adult worm from the gill chamber of Sebastodes schlegeli (Hilg. ) from the region of Vladivostok (Sea of Japan). Among the Mono- cotylidae the vagina is single with a ventral opening in a number of forms, however, it is divided into two ducts which open independently. Capsalidae either have a single vagina or it is often absent. Its opening is located for the most part laterally in the vicinity of the sex atrium and often it even opens into the latter in the direct vicinity of the penis and the opening of the uterus (Fig. 102). Among Microcothriidae the vagina is single or double. It is interesting that in the bifurcated duct of Lepto- bothrium pristiuri Gallien (Fig. 103 ) both of its apertures open into the special organs of the sex atrium. Acanthocotylidae and Gyrodactylidae do not have vaginal ducts. As a rule they are also absent among Mazocraeidae and Discocotylidae, and if they exist they are usually single. Among Acanthocotylidae the openings are paired. It is noteworthy that in Acantho- cotyle merlucci Beneden and Hesse there are two commisures uniting both vaginal ducts (Fig. 104); such a peculiarity has not been noticed in any other species of Monogenoidea. Annong Microcotylidae, Hexostomatidae, and Polystomatidae the paired vaginae start from the vitelline ducts. They 65 have either two lateral openings (Polystonnatidae , and part of Microcotylidae) , or they merge along the median line of the body and fornn a more or less elongated unpaired duct opening on the ventral side (part of Microcotylidae, Hexostomatidae). It is possible that Sphyranuridae are devoid of the vaginal ducts although according to the old data (Braun, 1889-1893) it is known that in Sphyranura osleri Wright there are two of them leading from the vitellaria but not opening outside and terminating blindly. In the given species these ducts play the role of the paired receptaculum seminis. Contemporary research (Alvey, 1933a, 1933b) subject the data concerning such structure in Sphyranura to doubts. Among the majority of Diclidophoridae the vaginal Fig. 103. Leptobothrium pristiuri Gallien, adult worm. Natural size 1.6 mm (According to Gallien, 1937). Fig. 104. Anthocotyle merlucci Beneden and Hesse, the diagram of the structure of the female sex system (According to Cerfontaine 1895, simplified). duct is absent; in rare cases it is paired, opening along the sides of the body (Diclidophoropsis). Hexabothriidae and Diclybothriidae have a divided vaginal duct which is closely connected to the vitellines and opens by paired apertures on the ventral side or along the sides of the body. The corresponding ducts of Chimaericolidae are most interestingly arranged. They are paired, they begin from the vitelline ducts and open by two apertures on the ventral side. At the same time and somewhat lower than the external openings of each vaginal duct, there is a junction with a special transversely-oriented vitelline gland. In such a fashion each duct has two efferent openings, one internal and the other external. The physiological significance of this is completely unknown, and such a structure is unheard of in any other species of monogenetic trematodes. 70 66 The apertures of the vaginal tracts are often complicated. Thus, among a number of species they form sucker -shaped funnels or a con- ven pad, very often instead of one opening there are a number of small ones, forming in their combination so to speak a small grill (grid, nobis) as is observed for instance in Polystoma integerrimum Froelich (Fig. 71). Among many forms there is a special chitinous armature of the vaginal aperture, as for instance among many Microcotylidae (Fig. 105). Finally, among many of the lowest Monogenoidea the terminal portion, which is sometimes a very significant part of the entire vaginal duct, has the shape, of a small chitinous pipe or funnel (Fig. 106). OJmm Fig. 105. Microcotyle sp. from the gills of Sebastodes schlegeli (Hilg. ) from the region of Yablochnoii (Southern Sakhalin, Sea of Japan). Fig. 106. Ancylodiscoides magnus Bychowsky and Nagibina, from the gills of Silurus glanis L. from the Delta of the River Volga. Chiti- nous armature of the vaginal duct. The genito -intestinal canal (canalis genito-intestinalis) exists in Polystomatidae, Sphyranuridae and all Oligonchoinea. In its structure this duct is somewhat reminiscent of the vitelline glands and also equipped with a ciliated epithelium and circular musculature, starts from the ovi- duct and extends, having greater or less length, and because of this being more or less curved, toward one of the intestinal trunks into which it opens. Sometimes however, the canalis genito-intestinalis opens into one of its transverse branches and not directly into the intestinal trunk. Among Protogyrodactylidae one observes a very odd-shaped peculiarity in the structure of the female sex system which appears as a distinguishing sign of that family. According to the description of Johnston and Tiegs (Johnston and Tiegs 1922), the vitellaria of these forms have a junction with the in- testinal trunks near the anterior end of the body which can be designated as the vitello-intestinal duct (canalis vitellario-intestinalis). This forma- tion undoubtedly is completely unique and cannot be considered homologous to any duct of the other Monogenoidea (see however page 360 ). p. 71 67 I • • On the question of the homology of the canalis genito-intestinalis and all of the vaginal ducts of flatworms, there exists considerable litera- ture in which are expressed the most varied points of view. According to one of them, the vaginal duct of Monogepoidea is homologous to the one in Turbellaria and Cestoidea and to Laurer's canal of Trematoda .whereas the canalis genito-intestinalis of Monogenoidea is similar to the one among Turbellaria. These points of view, with certain alterations, are held by Bresslau (Bresslau, 1928-1933) and Reisinger (Reisinger, 1923) and also Fuhrmann (Fuhrmann, 1928) and a number of other researchers. Others, as for instance Goto (Goto, 1894) and Looss (Looss, 1893), consider that the vagina of Monogenoidea corresponds to the uterus of Cestoidea, where- as the canalis genito-intestinalis c orresponds to Laurer's canal of trema- todes. Finally, a well-known authority of digenetic trematodes, Odhner (Odhner, 1912-1913) supposes that the vaginal duct of Monogenoidea is not homologous among the various species and that the vaginal duct emanating from the ovary represents the true vagina and that the duct emerging from the vitelline reservoir or from the vitelline ducts is a sui generis forma- tion which he designates as the ductus vaginalis. In connection with this, Odhner considers that the ductus genito-intestinalis corresponds only to the true vagina of Monogenoidea and also Laurer's canal of Trematoda. The system of Monogenoidea (see further page 336 ) proposed by Odhner appears to be the result of this point of view. We think that the vaginal duct of Cercomeromorphae is a for- mation homologous to that among Turbellaria. Also from our point of view the homology of the canalis genito-intestinalis of Monogenoidea and Tur- p. 72 bellaria cannot be subjected to any doubt. As for the connparison of the canalis genito-intestinalis and the vaginal duct with Laurer's canal of Trematoda it appears to us more reasonable to compare the latter with the vaginal tract of Cercomeromorphae. The views of Goto and Looss on the homology of the vagina of Monogenoidea and the uterus of Cestoidea do not withstand serious criticism. There is no doubt that it is a result of their being carried away by the convenience of comparison of the inter- relations of the ducts of both groups, but this point of view cannot be recog- nized as correct. Finally the point of view of Odhner has, at first glance, a serious basis; however, in the light of the present level of knowledge of Monogenoidea this view appears erroneous. The fact is that he established two suborders of Monogenoidea (which he accepts as an order). These two suborders, Monopisthocotylinea and Polyopisthocotylinea, differ by the fact that in the second there is a d uctus genito-intestinalis (vagina) and ductus vaginalis, whereas among the former there is only a vagina, however, as Fuhrmann correctly points out, we encounter among the first group of Odhner those relations which this author consider characteristic only for the secnnd group. Thus, for instance among Tristoma there is a ductus v aginalis according to the terminology of Odhner, but there is no canalis g enito-intestinalis. We noticed similar relations among a number of other Capsalidae and among part of Monocotylidae and so forth. Undoubtedly, 68 it is possible to find almost all transitions between the typical vagina accord- ing to Odhner and ductus vaginalis. Because of this we have no right to con- sider these formations as not homologous and consequently Odhner's point of view also appears to be erroneous. The receptaculum seminis occurs among representatives of all groups of monogenetic trematodes. Often how- ever it is also absent. It represents a special widening which serves for the retention of sperm and its location is varied. Sometimes it is simply a widening of the oviduct. In a number of speclesthe receptaculum seminis lies along the vaginal duct or is even functionally replaced by widening sections of the latter. There are no designations for the various types of receptacula seminis -, however, one must recognize the receptaculum seminis oviducti and the receptaculum seminis vaginalis as not homologous formations. The obtype into which the ductus communis passes represents the place of the formation of the eggs. Usually it is powerfully developed and separated from the duct which opens into it and also from the uterus, if the latter exists, by powerful sphincter-shaped muscular fibers. The form of the obtype varies, it can be rounded, egg-shaped, pear-shaped, etc., which basically corresponds to the shape of the egg which is formed therein. This ootype can be considered as an odd-shaped mold for the "stamping" of the eggs. Into it open numerous monocellular glands called shell glands or Mehlis' glands. Among a majority of species they are sharply developed and often divided into two groups which are variously colored on the slides. This can be observed with special clarity among Polystoma integerrimum Froelich. The function of these glands is not completely clear (for more details on this see pages 85 and 87 ). Among a number of Monogenoidea the ootype opens directly into a sex cloaca and the egg which is formed passes from the obtype, after a certain period of time, into the surrounding nnedium without prolonged delay in the body of the parasite. In other forms a more or less long uterus, which contains the fully formed eggs for a certain time, starts from the obtype. In such a fashion among some forms, the ob'type functionally serves as the uterus and in other types as both. One must note that this peculiarity does p. 73 not have important phylogenetic significance. Apparently the absence of the uterus is a primary phenomenon but among a number of forms, even highly organized ones, there is only an obtype. It is interesting that, during the time of embryological development of Polystoma integerrimum the so-called "gill form" has only an obtype, whereas the form from the urinary bladder of the frog has a well-developed uterus (see page 185 ). The uterus can be of variable length from comparatively short to very long and very curved and in a majority of species its curves lie across the body and only in Chimaericola are located longitudinally (Fig. 107). Among many forms the uterus is sac -like. Characteristic among some is the distribution of the eggs in a packet, whereas among the 69 ¥ majority they are arranged one after the other, of the uterus is similar to that of the oviduct. The histological structure For the convenience of description the structure of the eggs is described in the chapter on embryology (Fig. 89). The only viviparous family, Gyrodactylidae, sharply distinguishes itself from all other Mono- genoidea by the structure of the female sex system. The most stuffied sex system is that of Gyrodactylus (Fig. 12). This genus is charac- terized by presence of the ovo- vitellaria C'Keimdotterstock" of the German authors) and the absence of vitelline glands. Also in connection with this, the egg cells of Gyrodactylus, in con- trast to all other nnonogenetic trematodes, are fairly richly supplied with yolk although the feeding of the embryo which is developing within the uterus takes place apparently basically by way of the liquid alimentary substances which penetrate from the body of the wornn into the uterus. Besides the indicated peculiarities , among Gyrodactylus the vaginal and genito- intestinal canals are also absent. Undoubtedly the simplified structure of the sex System of these species is a secondary phenomenon and even the presence of the "ovo- vitellaria" which often occurs among Turbellaria, should not be considered as a primary primitive peculiarity. Fig. 107. Chimaericola leptogaster (Leuckart), diagram of the structure of the sex system (According to Brink- mann, 1942). In conclusion, it is neces- sary to note with regret that the level of the morphological study of monogenetic trematodes is still very low which undoubtedly hampers attempts at formulating a system to a signifi- cant measure. 70 CHAPTER II BIOLOGY OF MONOGENETIC TREMATODES The locations of monogenetic trematodes are quite diversified. p. 74 As is known, they parasitize mainly sharks, skates, holocephalans and bony fishes, amphibians and reptiles, and in addition, parasitic isopods, and are also known to exist on cephalopods and aquatic mammals. The parasites of fishes are found on the gills, in the gill chamber ajid buccal cavity, on the surface of the body, on the fins, in the cloacal cavity and in its vicinity, in the ureters and the body cavity, and finally, as an exception, in the heart. The majority of monogenetic trematodes para- sitize the gills and may be located very differently thereon. A majority of the species occur on the gill filaments, a few species of Gyrodactylus are located on the gill rakers, and a number of Monocotylidae and Capsalidae on the lateral surfaces of the gill arches, mainly on Elasmobranchii. The parasites which occur on the gill filaments are distributed differently. First of all, many forms occur on all four gill arches of the fishes and five to seven arches of the shark-types whereas others locate on the second and third arches in most cases or even exclusively. Thus, as a rule, a number of species of Mazocraeidae do not occur on the fourth arch and very seldom occur on the first, even in the case of relatively high levels of infection. Different species have favored places of location within the limits of a single gill arch. Some species (many Dactylogyridae and others) are located along its entire length, while others are either located only in the middle (for instance Diplozoon), or at either end (on the anterior end, for instance Monocotyle and the posterior, Nitzschia). Likewise the lo- cation in relation to the length of the gill filaments varies among different species. Thus, as a rule, Dactylogyrus anchoratus Dujardin settles at the base of the gill filament, whereas Dactylogyrus vastator Nybelin, on the other hand, settles at their very tips. Very often "concomitant" (ternns of V. A. Dogiel) species of Diplectanidae, Mazocraeidae and others can be easily distinguished by their location on the gill filaments. Monocotylidae and Capsalidae live mostly in the gill and buccal cavities. Representatives of the genera Benedenia and Capsala and others which live in the gill chamber usually are located on the interior surface of the operculum near the posterior bases of the gill arches. The worms lo- cate differently in the buccal cavity. Thus>for instance, Nitzchia sturionis (Abildgaard) occur in the lips, the palate, the tongue and sometimes even in the beginning of the esophagus, and certain Monocotylidae - -quite to the contrary- -live only on the surface of the palate. 71 Many species are encountered on the surface of the body, among these are Microbothriidae , many Monocotylidae and Capsalidae, Acantho- cotylidae and a number of Gyrodactylidae . The latter settle mainly on the p. 75 surfaces of the head, whereas Acanthocotylidae settle on the ventral and dorsal surfaces of the body. Monocotylidae and Capsalidae settle on either side, more or less indifferently, whereas Microbothriidae settle, apparently preferably, on the dorsal sides of the body of their hosts. Many lower Monogenoidea, mainly Gyrodactylidae and more rarely Dactylogyridae live on the fins. In addition, Calceostomatidae cer- tain Microbothriidae and also, where found, Monocotylidae and Capsalidae usually act as parasites on the fins. The species which act as parasites of the fins occur nnore often on the pectoral, than the dorsal, and more rarely on the caudal, ventral, and anal fins. Calicotylinae inhabit the rectal cavity and its vicinity among shark-type and holocephalan fishes. Until the pre- sent time only three species of Acolpenteron parasites of Cobitidae, Cato- stomidae and Centrarchidae were discovered in ureters. The special monogenetic genus Dictyocotyle (D. coeliaca Nybelin) parasitizes the body cavity of certain types of skates. Until the present time the only type found in the bood system is Amphibdella torpedinis Chatin. Ruszkowski (Ruszkowski, 1931), studying Torpedo ocellata Ruszkowski and T. nnarmorata Risso at the Naples Zoolo- gical Station, found adult worms in eight specimens of the first species (or about 35 per cent of those examined) and eggs in twelve individuals (or about 50 per cent); among T. marmorata only eggs were discovered in the heart. In this connection numerous worms were found in the normal habitat, that is the gills. Ruszkowski supposes that either the larvae which emerge from the eggs .penetrate into the blood system and there reach maturity and then lay their eggs while the newly acquired larvae perish or the adult worms penetrate the blood stream (with the help of the head glands?) and there remain without changing morphologically, but adapting themselves to the new conditions. Indisputably, one must consider such location aberrant. The parasites of amphibians and reptiles, i.e., representatives of Polystomatidae and Sphyranuridae, settle on the skin, gills, buccal cavity, under the eyelids and in the urinary bladder. The only species indicated for mammals, Oculatrenia hippopotami ,Stunkard, was described from the eye of a hippopotamus (see page 219 ). The parasite of cephalopod moUusks-- Isancistrum loliginis Beaughamp lives in the gills of Loligo media Linne'T Representatives of Diclidophoridae are encountered on parasitic Isopoda (for instance Choricotyle charcoti (Dollfus) on Meinertia oestroides or Choricotyle snnaris Ijima on the caudal segment of Cymothoa sp. sp. ); however, we are not inclined to consider these cases as specifically para- sitic action because the same types of Diclidophoridaeare encountered on the gills of fishes which are the hosts of these Isopoda. 72 As a rule monogenetic trematodes locate on the body of their host by attaching themselves by the posterior ends, and in normal con- ditions have little relocation movement or even do not change their location at all. Many species, however, are completely deprived of the ability to transfer .either because of a special structural arrangement of their attach- ing apparatus, or as a result of the growth of tissues of the host which sur- round the part of the body of the parasite and finally attach the worm for its entire life to a fixed position (Fig. 108). Under certain conditions, mainly unfavorable ones, many of the small worms (Dactylogyridae , Tetraonchidae and others) as well as the large worms (Monocotylidae , Capsalidae and others) move along the body of their host fairly actively. This transfer takes place with the help of the attaching apparatus of the posterior and anterior ends, and resembles the locomotion of leeches. The worm, which starts to move, first attaches by its anterior end, having stretched it in the direction of movement, and then, having attached itself, draws the entire 76 Fig. 108. Dactylogyrus iwanowi Bychowsky, adult worm sitting on the gills of Leuciscus brandti Wal. from the region of Vladivostok (Sea of Japan). On the left normal gill filament. body to the anterior end, again attaches itself by the posterior end, and re- peats the same nnotion (Fig. 109). It is not without interest to note that the strength of attachment of monogenetic trematodes by means of the anterior and especially the posterior end is very great. Thus, Dactylogyridae, which have been isolated into a saltshaker (some type of experimental vessel-- perhaps similar to a stender dish?, nobis) and which have attached themselves to it, withstand a fairly strong stream ot water from a pipette; apparently the attachment results from a sticky secretion of the glands from the posterior end of the body because the hooks cannot play a significant role under such conditions. Certain large forms, for instance Nitzschia sturionis (Abild- gaard), which have a powerful sucker attach themselves with such force that it is easier to tear the worm in two than to piill it from its place of attachment. 73 In the latter case and cases similar to it, it appears that the basic role is played by the cavity which is created as a result of the contraction of the muscles (in the posterior attaching apparatus, nobis) and which has less pressure in- side than outside. This is substantiated on the one hand by the swelling which remains on the body of the host (after the worm detaches or is de- tached, nobis ) similar to the ones resulting from medical jars (suction jars, nobis ) and on the other hand by the fact that if a very thin capillary, which allows passage for the water from the outside, is placed under the disc of the attached worm, there is little difficulty in removing the wornn,and in most cases it will fall off itself. ^•'^ j2^^=^^ Certain sections of the dis- sertation of N. A. Izumova (1953) were dedicated to the questions of behavior among monogenetic trema- todes on the gills of their hosts. While studying the influence of the oxygen content of the water on Dactylogyrus solidus Achmerow and D. vastator Nybelin, she suc- ceeded in showing that the change in the quantity of oxygen in the con- tainer leads to a change in the lo- cation of the first of these types. Thus, with a decrease in the oxygen content of the water D. solidus actively move to the ends of the filaments of the first and fourth gill arches concentrating on their ventral sections --places of the best aeration and conversly with an in- p. 77 crease in the oxygen content the worms return to the places of their original location, that is, to the middle and lower parts of the filaments of the second and third gill arches. The data of Izumova show that this is connected with the conditions of aeration of the different sections of the gills. As re- gards D. vastator, the change of oxygen supply does not cause a change in the location of the worms; apparently these worms are much less demanding of conditions of aeration. The species which are not capable of motion because of special arrangements of attaching apparatus, are encountered nnainly in the highest Monogenoidea, but they are also present among the lowest. Thus, Diplec- tanum similis Bychowsky, which parasitizes near the bases of the gill fila- ments of Corvina nigra Salv. , has such a distribution and arrangement of connecting pieces of the middle hooks of the attaching discs that it is deprived of the possibility of active transfer (movement, nobis) and at best can only Fig. 109. Nitzschia sturionis (Abild- gaard), locomotion of the worms along a flat surface. Sketches made on the Island of Sara (Caspian Sea) from the worms discovered in the buccal cavity of Huso huso (L. ). 74 detach itself from one gill filament and attach itself to a neighboring one. Many Microcotylidae with a large number of attaching clamps are practi- cally devoid of the ability to transfer, although the separate clamps can easily change their position. As a matter of fact, among these species the adhesive glands of the posterior end are completely undeveloped and they are not in a condition to attach themselves to smooth glass surfaces with their posterior ends. This applies to the adult individuals, wnile the young ones still possess attaching capability. The reactions of the host to the attachment of monogenetic trema- todes can be very different. With the attachment of worms by means of hooking apparatus, we often observe significant injuries to the body of the host. On the gills of fishes strongly infected by Dactylogyridae , one can easily notice numerous hemorrhages and ulcerations of the epithelium. It was already nnentioned that during the attachment by means of the discs, large round bruises and swellings are formed. At the same time, significant ulceration of the tissues of the host also takes place in serious cases of this type. The highest monogenetic trematodes which attach themselves by means of clamps apparently inflict the least damage. In a number of cases the irritation of the tissues of the host under the in- fluence of the presence of the worms will cause growth of epithelium and con- necting tissue, as a result of which significant swellings develop. With this, anaong a number of hosts the tissues will grow over and around the attaching disc of the worm, and among some, special growths are formed on which the parasite re- mains and these growths often fall off carrying the worm with them, and in this fashion, clear the para- site from the host. We see ex- amples of fixation by the tissues of the host among Dactylogyrus iwanowi Bychowsky (Fig. 108) and Linguadactyla growths. Magnification 30 times. molvae Brinkmann. The second type (According to Wunder, 1929). of changes of the tissues of the host Fig. 110. Linguadactyla molvae Brinkmann, adult worm on the gills of Molva dipterygia elongata from the south of England (Atlantic Ocean). Natural size of worm about 3 mm. Fig. 111. Dactylogyrus vastator Nybelin, adult worms on the gills of the carp, forming pathological p. 78 75 is easily observed in mass infestations of the young of cultured carp by Dactylogyrus vastator Nybelin (Fig. 111). Pathological changes under the parasitical action of monogenetic trematodes can bring with them a very dangerous character for the host. We know that with a strong infection many species of Monogenoidea can cause 'death of the host, and under very unfavorable conditions (e.g. overcrowding of fishes, etc.) can also even cause mass epizootics which have great significance in pond culture of fishes. Thus, in Silesia numerous epizootics of carp caused by Dactylogyrus vastator Nybelin caused millions of losses to pond farms. A very well-known serious incident of the mass destruction of the small Aralsk sturgeon in a natural reservoir (occurred, nobis) as a result of insufficiently planned attempts at acclimatization of the stellated sturgeon in the Aralsk Sea which carried Nitzschia sturionis (Abildgaard), which was never encountered there before, with it into this reservoir (or body of water, nobis) . (For greater detail see Lutta, 1940). There is reason to believe that during the attempts at acclinnatization of Gwiniads (Gang Fish, nobis) the Discocotyle sagittata (F. Leuckart) which parasitize them can cause undesirable epizootics. The incidence of occurrence of parasites on their hosts is still very insufficiently known for a majority of monogenetic trematodes. It is not something constant for each species, but depends on a number of various factors: geographic situation of the region of research, the location of the latter in the range of the host, or the time of the year, or the biolocy of the host, etc. Very often the parasite which is encountered on 100 per cent of the hosts m the main portion of the range of the latter is encountered very seldom near the edge of the range. For instance, Dactylogyrus simplici- malleata Bychowsky in the Delta of the Volga is encountered in 100 per cent of the hosts, while in the Bay of Finland it is a great rarity. Ancylodiscoides siluri (Zandt) in the lower part of the Volga is encountered on 100 per cent of the Sheetfish (Siluris glanis , nobis), whereas above Seratov it is encountered only in rare cases. For the most part the majority of representatives of Dactylogyridae are encountered on 100 per cent of the fishes in the middle of the range of the host in the sunnmer, and in the winter, as a rule, not p. 79 more than 20 to 25 per cent. On the other hand, among the same family a number of species are very rarely encountered throughout the year, as for instance Dactylogyrus similis wagener on the Roach of the Leningrad region. For many Monogenoidea the incidence of occurrence changes to a great degree depending upon the age of the host. Thus, nunnerous Gyrodactylus which parasitize 100 per cent of the young fishes are discovered in the adult only in exceptional cases. Protancyrocephalus strelkowi Bychowsky is a typical juvenile parasite of the flounder, among the young of which it occurs in 100 per cent of the cases, whereas it is practically absent among the adults. On the other hand, many monogenetic trematodes are completely absent in the young individuals of the host and infest the adult fishes in large percentages. Thus, Diclybothrium armatum Leuckart is not encountered on young sturgeon and very often occurs on from forty to eighty per cent of the adults. According to our studies, this parasite is not encountered on Sterlets 76 20 centimeters in length, on Stellated Sturgeons up to 45 centimeters in length, on Sturgeons up to 43 centimeters in length; according to the data of Dubinina (1952) and of 184 Sturgeons and 16 1 Sterlets measuring up to 40 centimeters from the lower part of the Volga, only 1. 7 per cent were infected. Apparently the largest individuals were the most infected. In the autoreference of N. L. Nichiava's dissertation (1953) there is an indi- cation that 52. 94 per cent of the young Sterlets examined in the region of Seratov were infected with D. armatum . Unfortunately the author does not indicate the sizes of the fishes', it is thought that she had relatively large fishes -- which become infected first in natural conditions. Only yoxing individuals of herring and mackerel which are completely devoid of Mono- genoidea come to the Barents Sea near the region of the Murmansk Biological Station, whereas the adult individuals living near the shores of Norway and England are intensely infested by Mazocraes and Octostoma . It would have been possible to show a significant number of similar examples but we shall only indicate further that the dependence on the incidence of occurrence of the age of the host was well examined on Polystoma integerrimum Forelich by Zeller (Zeller, 1872a). His researches, which were done at the same time in a single place ,showed that frogs aged from 6 to 7 months are 90 per cent infected; that those aged one and one-half years, 33. 3 per cent ; those two and a half years old, 42 per cent ; and those three and a half years, 27 per cent; and those four and one -half years, 10 per cent. The salinity of the water exercises great influence on the inci- dence of occurrence. Thus ,in the freshened part of the Aral Sea we found Dactylogyrus simplicimalleata Bychowsky in 80 per cent of the cases and in strictly marine water--40 per cent, whereas in fresh water--93. 3per cent. Interesting studies were conducted by us on the lakes of the Bara- binskaya Steppe (Bychowsky, 1936a). The influence of salinity on the inci- dence of occurrence of Dactylogyridae on the fishes was clearly apparent. It was indicative that in the most saline parts of Bolshoi Chan and Mali Chan, the monogenetic trematodes were almost absent. Moreover, the only finding of Dactylogyrus nanus Bychowsky on Bream in Bolshoi Chan showed, during the checking of the material, that the infected individual of the fish had a different tempo of growth than all the others and undoubtedly came to Bolshoi Chan very recently and had not succeeded in freeing itself of the parasite. However, side by side with the species vvhich change incidence of occurrence depending upon the salinity, there are also species which behave quite in- differently to it. These are a number of species of Gyrodactylus parasitizing the Three-spined Stickleback which is infected by them both in fresh and ocean water. In addition to the existing direct observations on a number of regions, S. S. ShuUmann conducted very informative experiments at our request. He transplanted sticklebacks infected with Gyrodactylus sp. sp. from fresh straight into sea water and observed that after a short peoriod p. 80 of "salt-shock" the worms continued normal movement and apparently did not experience any harmful consequences. Reverse experiments in retrans- plantation of fishes and worms from the sea into fresh water gave the same 77 results. We should also note that many species occurring on various hosts \ have varying incidences of occurrence for each one which is fully within the law (normal, natural- -in conformity with the established natural law or principles, nobis ).! Thus, Ancyrocephalus paradoxus Creplin is discovered in a considerable percentage on Lucioperca and in a very small percentage on Perca, The incidence of occurrence of Nitzschia sturionis (Abildgaard) on the White Sturgeon or Beluga (Huso huso, nobis) is always significantly higher than in the Stellated Sturgeon, Sturgeon and Small Sturgeon (Acipenser stellatus , Aci- pen-ser , and Acipenser nudiventris, nobis) . The intensity of infection of Monogenoidea fluctuates extremely among the various types. Certain species are encountered mostly in a few individuals per host, whereas others occur by the thousands on a single host individual. For instance, within the limits of one genus Gyrodactylus ; G. marinus Bychowsky and Poljansky are encountered on Cod in the Pacific Ocean by the thousands per host, whereas^ groenlandicus Levinson is encountered on Bullhead (Cottus) only in a few individuals per host. The clarification of the factors which influence the incidence of occurrence should be considered very desirable because it will be possible , in this connection to establish rational nneasures controlling illnesses caused ^ by them under conditions of pond culture. I There is almost no information concerning the life span of mono- genetic trematodes. What is known without a doubt is that along with the j forms which live less than a year (a majority of Dactylogyridae , Gyrodactylidae) , | there are numerous types which live several years. Thus, Dactylogyrus I iwanowi Bychowsky lives not less than two years, which is evident from its life cycle (see page 110 ). Diplozoon paradoxus Nordmann begins to lay eggs , only in its second year and apparently lives not less than a year after the first laying. Mazocraes alosae Hermann .which parasitizes Caspian herrings, infects the fish at the age of not less than a year plus, and perishes together with the host at the age of two to three years during the death of the fish after spawning. Polystoma integerrimum Froelich which infects frogs only in the tadpole stage, is often encountered among frogs which are six years old and thus lives not less than five to six years under favorable conditions. On the other hand, a form of this same P. integerrimum which lives in the gills of tadpoles in the semi-adult condition (see page 121 ) has a life span of not more than one and one half to two months. On the basis of the data of life cycles on Monogenoidea, one can expect that generally the majority of the highest forms have a polyannual existence, although this is not significantly substantiated by specific observations. The continuity of life of the com- I mercially important Dactylogyrus vastator Nybelin has not been fully eluci- | dated up to this time in spite of numerous studies of its biology. According I to the experiments of N. A. Izumova, which were recently carried out, the normal span of life for the majority of D. vastator fluctuates between 25 and 40 days, however, it must be taken into consideration that certain individuals 78 I without a doubt live through one winter and consequently perish at the age of not less than 6 to 7 months. The span of life of monogenetic trematodes after the death of the host is generally not great. We happened to discover live worms on dead fishes not later than 24 hours after the death of the host. Usually monogenetic trematodes do not abandon the body of the host under any con- ditions, but certain species from the skin and fins possess this capability. Thus, according to our observations, many Gyrodactylus leave the fish after certain periods and for IZ to 14 hours move in lively fashion along p. 81 the bottom of the reservoir (or container, nobis ). It is possible that they are not deprived of the ability to infect new individuals of the host. As re- gards the survival of the worms in artificial conditions without food (in salt shakers with constantly replenished and aerated water), the periods are also insignificant. Bear (Bear, 18Z7) shows that Nitzschia sturionis (Abild- gaard) lives not more than 24 hours; this form lived somewhat longer --up to 30 hours -- in our experiments. According to Thaer (Thaer, 1850), Onchocotyle appendiculata (=Squalonchocotyle species, according to present nomenclature) lives in water not more than 36 hours. Capsala molae (E. Blanchard) can live in water without food up to 14 days (Braun 1889-1893), Diplozoon paradoxunn Nordmann from 3 to 9 days (in the last case^ by being fed with fresh fish blood). Dactylogyridae, Gyrodactylidae, and Polystomatidae live not more than 48 hours in water (without food). Usually they perish at the end of 24 hours. Feeding of monogenetic trematodes takes place on the body of the host and at its expense. During the time of feeding, the worms custom- arily attach themselves by the anterior end and less often perform scraping motions. Among the majority of forms the seizure of food takes place mainly with the help of the pharynx, more seldom of the buccal funnel or buccal suckers. As has already been indicated, the pharynx is capable of pro- truding in a manner resembling the pharynx of Turbellaria; usually it is equipped with a number of powerfully developed glands which apparently play a role in the preparation of food before its seizure inside the digestive system. As food, monogenetic trenraatodes use epithelial cells of the cover- ing of the host, secretions of the glands, and blood. Part of the species feed by all, and some only by one of these types of food. For the most part Dactylogyridae feed on the mucous secretions of the skin and its cells, although a number of species, as for instance Dactylogyrus vastator Nybelin, Tetraonchidae, Calceostomatidae , Monocotylidae , certain Tristomidae and other families close to them feed preferably on the blood; Gyrodactylidae, almost exclusively on mucous and epithelial cells; Polystomidae and Sphyra- nuridae, mainly on the blood. Numerous highest Monogenoidea also feed pre-eminently on the blood. The egestion of undigested food remnants takes place also through the buccal opening and apparently after indeterminant periods following reception of food. 79 J The reproduction of monogenetic trematodes can take place during fixed (or limited, nobis ) periods, or it can be nnore or less extended in time. As a rule reproduction does not take place during the winter among fresh-water forms, whereas among marine forms this occurs in a number of cases. The majority of Dactylogyridae and Tetraonchidae apparently reproduce more or less steadily during the course of the entire warm period, but the conditions of temperature and oxygen diet influence the tempo of reproduction to a great extent. Thus, under existing conditions of the middle of the European U. S. S. R. , common species of Dactylogyrus , Ancyrocephalus and Tetraonchus produce eggs beginning from April up to September and, depending upon the nature of the year, much later. We do not have any data about the time of reproduction of Monocotylidae and Microbothriidae and a number of other Polyonchoinea. According to our data, Capsalidae reproduce mainly during the first half of the summer months. The presence of embryos among Gyrodactylidae is observed all year round, although their birth is apparently adapted to the warm months. Among the highest species, a part reproduces during all the summer months, and some also in the winter months, whereas others have a fixed period p. 82 connected with the peculiarities of the life cycle of the parasite and of the host. For instance, among Polystoma integerrimum Froelich the repro- duction takes place only during a very short period (directly after the emergence from the places of hibernation), and lasts about a month --at the latitude of Leningrad from the end of April to the beginning of May ( sic) . The gill forms of Polystoma integerrimum reproduce during the entire period of its maturity until the end of life^ which coincides with the end of the metamorphosis of the tadpoles, that is, one and one half to two months Let us note that the species which reproduce periodically and, in this connection which lay a relatively much larger number of eggs in a short period of time than the species with extended laying, in a majority of cases have a longer or more voluminous uterus, sometimes containing a great number of eggs (among P. integerrimum more than 100 eggs, among Microcotyle gotoi Yamaguti up to 150). For more detailed information concerning repro- duction see pages 105-137. Among species with extended periods of fertilization, the activity of the male eex system takes place more or less steadily during the entire warm period of the year. Among such species during that time we always find all or almost all stages of spermatogenesis in the testes, and in the seminal ducts and in the vesicula seminalis a greater or lesser number of ripe spermatozoids ready for fertilization. Amongspecies which h^ve a more or less short period of fertilization the male sex system acts periodi- cally. Thus, among P. integerrimum increased spermatogenesis begins in the period which follows the laying and ends at the end of the summer, and at that time almost the entire testis and partially also the vas deferens is filled with ripe spermatozoids. The latter are preserved in this shape until spring and during the period of fertilization are almost completely used up. During the time of fertilization the vas deferens among Polystoma is strongly 80 .I'l inflated from the mass of spermatozoids which fills it to excess. During all the remaining tinne it is strongly narrowed and its interior lumen almost completely declines. The prostate glands are also more intensely filled during the period of reproduction. The fertilization of worms is achieved through cross- or self- fertilization. Cross -fertilization can occur by means of copulation or without it. Among Monogenoidea which have vaginal ducts insemination occurs through them; among forms without vaginal ducts, just as among digenetic trematodes, it takes place through the uterus. However, the possibility that certain types with vaginal ducts can also be inseminated through the uterus is not excluded. Copulation of Monogenoidea is known only among a small number of species because of the difficulty of obser- vation. This process has been studied best of all among _P. integerrimum . Their copulation takes place in the period directly preceding the egg -laying and sometimes during it. Both worms taking part in copulation remain attached to the urinary bladder wall, they embrace with the anterior ends and alternately introduce their copulatory organs into one or the other of the vaginal apertures and during an hour there can be twenty copulations. The role of the male and of the female is alternately borne by both: now one j jj j plays the role of the male, and the other of the female, now the reverse. Because among Polystoma the vaginal apertures on each side of the body are in the shape of a sieve plate, the copulatory organ cannot be fully intro- duced into them but only its chitinous hooks. The period of individual acts of copulation is rather significant; it lasts from one -quarter to one -half minute. Zeller (Zeller, 1876) observed the process of copulation of Poly- stoma and so did we. We have conducted special experiments, the method- ology of which is not without interest. In order to observe the behavior of p. 83 Polystoma in natural conditions we immobilized the frog and then opened its ventral cavity, placing the operated animal into a little bath of physiological solution. After the opening of the ventral cavity we introduced the physio- logical solution by pipette through the anal opening into the bladder in such quantities that the bladder would be fully distended and as a result com- pletely transparent. The Polystoma contained therein was studied under the binocular microscope and the observations could be conducted up to 48 hours without any noticeable deterioration in the condition of the host and of the parasites. Wilde (Wilde, 1937) described copulation among Dactylogyrus macracanthus Wegener. It lasts from fifteen to twenty minutes and takes place after the worm which acts as the male has already laid its eggs. The worms are seldom observed in copula. During copulation a sperma- tophore is introduced into the vagina and the receptaculum seminis is filled with sperm. However, in spite of numerous attempts we never succeeded in observing the copulation of different types of Dactylogyrus ; as a result of i. . this we are inclined to think that this process takes place not as simply as '" ' it is described by Wilde, and probably is of a different nature. Wi 81 Cross -fertilization without the help of copulation (this method was first indicated for digenetic trematodes by Sinitsin in 1906) can take place among certain speciesliving in the regions of low concentration and their spermatozoids are ejected from the copulatory organs of one indi- vidual of the parasite and reach the sex glands of the other through the surrounding medium. In addition to that, there is reason to believe that a number of species form spermatophores (apparently many Dactylogyridae, and apparently a number of highest species). Self-fertilization among Monogenoidea occurs very often in all families. It takes place either by means of self -copulation (this, however, is subject to doubt), or without copulation by means of cross- fertilization through the surrounding medium. Certain species are mainly self-fertilizing (for instance Dactylogyrus iwanowi Bychowsky), while a large majority has recourse to this method only where cross -fertilization is impossible. Thus for instance during the presence of one parasite in the urinary bladder of the frog (and this can be almost in 50 per cent of the cases of infection Polystoma integer rimum Froelich), the copulation which we just described fertilizes itself, and no delay in egg -laying or abnormal development of eggs has been noticed. The adaptation to cross -fertilization among Diplozoon paradoxum Nordmann is completely different. The adult forms of this species are encountered only grown in pairs in a criss-cross fashion. In them the ducts of the female sex system of each individual grows together with the ducts of the male sex system of the other so that for the entire life the possibility of cross -fertilization is insured and conversely self-fertilization is excluded (Zeller, 1872b). The same peculiarity is possessed by other species of the genus Diplozoon. Apparently, nevertheless, cross -fertilization occurs nnuch more often than one can suppose and, of course, than can be observed. It can be guaranteed by the alternate ripening and development of male and female sex products, which was observed by a number of authors. Thus, Sproston, (Sproston, 1945b) saw this among Octostoma scombri (Kuhn). She considers that among the worms there are at least three phases during their lives when the male systemi acts predominantly and two when the fennale predominates. As a rule the male system begins to function first; our data also substantiate this. The functioning of the female sex system falls into a number of p. 84 successive phases. Thus the activity of its separate parts takes place, now during the time of the reproductive period, now beyond it, and finally in both. As an example of the activity of the female sex system we shall analyze it among Polystoma integerrimum, a specie which was especially studied by us for a number of years. Everything that will be said further about this can be extended to the rennaining Monogenoidea, with the exception that among specieswith an extended period of laying these stages can coincide in time and part of them, specific for Polystoma, is completely excluded. 82 Toward the period of egg -laying which begins after the winter months, the ovary of Polystoma from the urinary bladder of the frog is in a condition of full readiness for the mass discharge of ripe egg cells. It is almost completely filled with them and only a small intensely-pressed channber near its upper end which is slightly curved is filled with cells in various stages of oogenesis and these are in the "frozen" condition, un- changing for a long period. The envelope of the ovary during this time is thin and membranous. Its separate cells are noticeable only with great difficulty. Just before the very beginning of egg-laying, a process called by us "excision" of the eggs takes place when the egg cells change from the polygonal, as they are during the winter period, into the rounded shape. During the "excision" of eggs not the entire cell is rounded (?, nobis), a part is rejected and completely taken, out as a rule through the genito- intestinal duct into the intestine. The reasons and significance of this re- jection of a part of the cells are completely unclear to us. During the time of the laying the ovary frees itself of a large mass of egg cells, in con- nection with which it even changes its shape to a more extended one. To- ward the end of egg -laying only sex cells which begin to develop strongly remain in the ovary, and they are in different stages of oogenesis. In addition, a certain number of oocytes which were not ejected remain in the ovary after the laying, as a rule in large or smaller quantity. The pro- cess of increased oogenesis, which begins at the end of the laying, continues during the entire summer and terminates in the fall before the departure of the frogs for hibernation. At this time the ovary acquires the same aspect as before laying and remains in this condition until the following reproductive period, that is until the spring of the following year. Parallel to the pro- cess of oogenesis, immediately after the laying an increased process of de- generation of unused oocytes takes place. They gradually fall apart and are seized by the cells of the envelope of the ovary which develop strongly at that time and in which the remnants of the oocytes are digested. The pro- cess of degeneration and seizure of the remnants of the egg cells by the envelope was observed by us among species with long reproductive periods, as for instance Nitzschia sturionis (Abildgaard). During the period of egg- laying the vitellaria, which develop extremely powerfully and occupy the main part of the animal, quickly expend the vitelline cells, and after that they develop intensely again during the summer and toward the winter they are already in the ready state among Polystoma. Among species with an extended period of laying, the expenditure and replenishment of the vitelline cells takes place at the same time. During the period between layings, all the ducts of the female sex system are in the deflated state and empty, whereas during the period of egg -laying they are strongly swollen because they contain some other fluid in addition to the sex products (see further). After copulation the sperm enters into the strongly inflated middle section of the vaginal ducts which among Polystoma functionally replace the receptaculum seminis of other forms (it is interesting to compare it with the blind vaginal ducts of Sphyranura which play the same role; see Jiowever,page 69 ). The expenditure of the sperm and of the vitelline and egg cells in forming the eggs takes p. 85 83 place gradually and is regulated on the one hand by the muscular widening of the oviduct which is located at the place of junction with the vitelline duct and which plays the role of a valve in front of the ootype, and on the other hand by means of extrusion of excessive sex products into the intestine through the genito-intestinal canal. Apparently this extrusion should be con- sidered as the basic and only function of the latter. All the sex products^ which in the ootype are surrounded together in determined portions by a shell and in the shape of eggs^are transferred into the uterus from which, after a relatively short time, they are extruded. The function of the uterus is clear; it serves as a place for the preservation of eggs which have not yet been completely formed or hardened and besides, among forms with "rationed" laying, and to that type Polystoma is related, as the place of collection of a determined number of eggs which are set aside at the same time. One must also remark about "shell" glands which forcefully extrude their secretions into the ootype around which they are located during the period of laying. Toward the end of the laying their contents are completely emptied and replenishment takes place gradually during the summer period. The significance of the "shell" glands nevertheless remains unclear. As was already indicated (page 72 ) they consist of two groups and consequently produce two different secretions -- liquids. If one can suppose that one represents fluid which fills the ducts and so to speak "lubricates" the sex products contained therein and first of all the eggs, then what is the function of the second? One can only think that, in spite of the existing views (see Goldschmidt, 1909), this secretion plays a certain role in the formation of egg cells (for more details see page 87 ). We should also indicate that among species without the genito- intestinal canal, the unused sex products are also extruded but through the uterus and they are thrown completely outside without any utility for the organism. In very rare cases, especially during the disruption of the activity of the sex system, we observed that unused sex products are ex- truded through the uterus, and among species with the genito-intestinal canals, particularly among Polystoma . Thus, summing up the data con- cerning the function of the sex system in Polystoma , we see that it takes place so to speak in three phases falling into definite periods: preparation for laying, the period of laying itself, and the "post-laying" recuperative period. We see such a distinct periodicity among the large majority of Monogenoidea which have polyannual existence; and among other species one observes the overlapping of one phase with the other and all the processes are more extended in time. 84 CHAPTER m DEVELOPMENT OF MONOGENETIC TREMATODES As was indicated, the formation of eggs takes place in the o'dtype p. 86 and the speed of their formation can sometimes be considerable. Thus, according to our observations, the time during which an egg is formed among Dactylogyrus vastator Nybelin fluctuates from 4 to 20 minutes, whereas among Polystoma integerrimum Froelich this period is sometimes decreased to one and one half minutes. The number of eggs deposited by a single indi- vidual monogenetic trematode is very great; this is true in equal measure of the species with short life spans as well as those with long. ones. Thus, among a number of species of Dactylogyrus the egg deposition continues almost the entire summer, and it is more or less uniform during this time. Very interesting are observations in the deposition of eggs of D. vastator which were conducted by N. A. Izumova. According to her very meticulously executed experiments, it was foiond that in surroundings which approach natural conditions^ vastator deposits eggs very intensively but not uniformly de- pending upon the age and the oxygen conditions of the milieu. Generally, we can expect that at normal oxygen levels worms which begin laying at the age of eight days after attraction to the host deposit from 4 to 10 eggs in a period of 24 hours at 12° to 18° C during the first ten days. A decrease in oxygen and a rise in the water temperature result in an increase in the number of eggs deposited. That is why it is so easy to acquire an intensive laying of D. vastator in artificial and obviously unfavorable conditions. Among Polystoma integerrimum Froelich, according to our observations in natural conditions, the eggs deposited during the spring egg- laying period reach 2,000 to 2,500 and on separate days the number fluctu- ates from a few to 1500. As observations indicate, certain individuals of P. integerrimum p roduce eggs more or less uniformly through a number of days, and others deposit at first a large number of eggs and then their laying is quickly curtailed and then completely stops. It is apparent from Table 1 which way the process takes place among different individuals which are found in the host singly and among several parasitizing the frog at the same time. The egg-layings, the data concerning which are given in the table, took place under experimental conditions at an earlier time than in nature, but their nature fully corresponds to this process under natural environ- mental conditions. The process of egg formation among monogenetic trematodes can be considered as almost completely unstudied. During the observations of development of eggs among Dactylogyrus we often"had eggs with already formed but still soft shells containing onlyihe egg cell. These eggs had open posterior ends and into them were poured, after a certain time, vite- lline cells and this infusion was accompanied by intense contractions of the p. 87 85 J cq < u 1—4 a; o u s £ ^H ^< (U 00 V S .2 to T) J3 o c c o O a • f-i > o c o to o Q PO in r d to (M Z a cm ^1 O o o Z u. o O . O 2 6 12 bO (M O . O o (M (T- a ■M m Q 00 CT^ I ^ O iTi ro o a; H Q 86 vitelline ducts. Very often .separate vitelline cells return to the vitelline ducts with the contractions of the uterus. After a certain period the eggs close, and at the place of the opening remains a little foot of the egg which lies behind the uterus at the place of junction of the vitelline ducts. In such a fashion, as much as can be ascertained by these intermittent observa- tions, the little foot of the eggs of Dactylogyrus appears not as an individual specially formed outgrowth but corresponds to the wall of the egg pressed and elongated like the "little nose" of an electric bulb," (Bychowsky, 1933). Views similar to the one described were observed in a number of other monogenetic trematodes, fresh water as well as marine. However, there is still much that is not clear. In the beginning, in the ootype the shell of the eggs, as is obvious from the preceding, has a soft consistency and only after a certain time hardens. This was noticed earlier by a number of re- searchers. Thus, Kulwiec (Kulwiec, 1927) writes that the egg of Dactylogyrus anchoratus (Dujardin) in the ootype (uterus by her terminology) is soft and during the contractions of the body changes its shape. There are different opinions concerning the formation of the egg shell. Some authors (predominantly of the last century) think that it is formed at the expense of glands which are now designated as Mehlis gland and formerly called shell, and others that the shell is formed at the expense of the "shell" secretion of vitelline cells and that the secretion of the "shell" glands is of no, or in extreme cases, of very little significance in this pro- p. 88 cess. The last point of view, substantiated by certain histological studies, appears to be more or less generally recognized at the present time. It appears to us, however, that this question cannot be considered as finally settled. First of all, there are no sufficient basest) maintain that the egg shell and its derivatives, that is the little foot and filament (see further page 90 ), are fully and always homologous. If this (explanation, nobis) is quite possible for eggs with a small foot and filament, on the other hand, it is easier settled negatively for the eggs with comnlex and strongly developed derivatives. Thus in the sections through fully formed eggs of Acanthocotyle verilli Goto, we see (Fig. 112) that the envelope of the egg is colored some- what differently than the posterior part of the little feet which apparently are formed at the expense of a different secretion than the envelope itself. In the formation of eggs of Diplectanum aculeatum Parona and Perugia, one can likewise observe that this process is sufficiently complex. The uterus is filled with a liquid which is possibly produced by the shell glands even before the formation of the egg. At first, the egg cell gets into the uterus and then the vitelline cells. The vitelline cells enter the uterus by portions and immediately after they appear in the narrowed first part of the uterus, the egg shell begins to form. After the cessation of the influx of the vite- lline cells and the formation of the shell , at the posterior end of the latter there remains an opening into which several vitelline cells pass back into the narrowed anterior part of the uterus. At this time around the cells which have come out, a little foot begins to grow further and further from the end of the egg in the shape of a hollow little pipe. Then the moment 87 comes when these vitelline cells fall apart, so to speak, and disappear and at this time the formation of the little foot ends. Its lumen is reduced either completely or in certain places, leaving small cavities. At that time the little foot is still lacking the little end star which is characteristic of the eggs of Diplectanum. The latte-r begins to form after the final for- mation of the little foot and apparently at the expense of some other secre- tions not connected with the vitelline cells. In this fashion, there is reason to believe that the egg shell is formed not only at the expense of the vitelline cells, but also at the expense of other secretions. These can only be produced by the "shell" glands, be- cause there are no other glands in the female sex system. However, one must recall, as was indicated (see page72 ), that the "shell" glands themselves are not homologous but consist of unicellular glands of dif- ferent structure and probably pro- ducing a different secretion. In the work of A. V. Ivanov (1952) on the structure of Udonella Si MM Fig. 112. Acanthocotyle verrilli Goto, cross section in the region of the uterus. Two sections cut through the eggs, and pieces of the little feet of the egg are seen in the uterus. Worms from the skin of Raja radiata Don. near the re- gion of Murman (Bering Sea). Explanation in the text. caligorum Johnston the ootype and the glands which enter it are described in significant detail and the author talks convincingly about indisputable participation of the secretions of one type of "shell" glands in the forma- tion of the envelope of the egg. We are inclined to think that this opinion can be substantiated by our data for monogenetic trematodes. Likewise, the data of A. V. Ivanov concerning the complex structure of the little stem of the egg of Udonella , which is the equivalent of the little foot of the eggs of Monogenoidea, fully corresponds to the data about the formation and structure of the little foot of Diplectanum , Nitzschia and other monogenetic trematodes. In connection with this, one must say that the similarity be- tween Udonella and Temnocephala indicated in the work of A. V. Ivanov by the characteristic of the gluing of the egg to the substratum by this secretion, which differs from the substance of the egg envelope, should be extended also to Monogenoidea because it is a characteristic which is common for all three groups. The formed egg consists of the envelope with its deri- vatives, of a relatively small number of vitelline cells, and of an egg cell against which the spermatozoid comes tightly. The latter usually lies with- out change until the deposition of the egg, because the fertilization of the egg cell takes place later and only in rare cases at the time of the presence of the egg in the maternal organism. 88 The shape of eggs of monogenetic trematodes is very different. It varies from almost spherical, oval or egg-shaped to pyramidal and even m.ore complex (Fig. 113). As a rule, the shape of the egg depends upon the configuration of the inner surface of the ootype and represents, so to speak, a molding in accordance with its form. The eggs of Monogenoidea can be easily oriented because on the upper end there is a more or less p. 90 Fig. 113. Eggs of monogenetic trematodes. A- - Diplectanum aucleatum Parona and Perugia (under the egg, the end feet of two eggs, greatly magnified); B--Mazocraes alosae Hermann; C- -Benedenia derzhavini (Layman); D- -Acanthocotyle verrill i Goto, group of eggs (with common bases!); E--Protoancyrocephalus strelkowi Bychowsky; F-- Diplozoon paradoxum Nordmann; G- -Microcotyle gotoi Yannaguti, deposition (mass, nobis ) of eggs; H- - Microcotyle gotoi Y amaguti (entire mass is deposited at one time ! ). noticeable operculum. In a majority of forms the eggs have offshoots of the shell located on the upper, lower or both ends. The majority of re- searchers group all of these sprouts under the common name, filaments of the eggs. In our opinion this is completely inaccurate because the upper and lower sprouts are formed differently and are not homologous to each other. We designate the sprout of the upper pole of the egg as the filament and the lower as the little foot. The little feet of the eggs can be very short in the shape of a small thickening at the anterior end of the egg (a majority of Dactylogyrus ); its location can be varied; either precisely along the axis of the egg, for instance Ancylodiscoides siluri (Zandt), or it can be more or less considerably displaced (for instance among Dactylogyrus wegeneri Kulwiec). The short feet are for the most part straight and devoid of I I 89 thickenings or widenings at the free end (for instance Ancyrocephalus). The longer feet can be of various lengths, sometimes they can even exceed the length of the egg several times (many Microcotyle ). usually they are equipped with a noticeable widening --a little platform at its free end. This little platform can be of an irregular shape (many Dactylogyridae) , or it can acquire a completely regular outline, as for instance among Diplectanum with a regularly 5- to 6 -pointed little star at the end of the little foot of the eggs. In a number of cases the end of the little foot forms a sharply curved, hook-shaped growth (for instance among Microcotyle gotoi Yamaguti). Usually the little feet of the eggs^ which have a consider- able length are more or less strongly curved and, more rarely, are com- pletely straight. The filament of the egg is of the same shape as the little foot. In a number of cases it is shorter than the little foot (for instance among Mazocraes), or more often it is absent (majority of the lowest Mono- genoidea). However, among many marine types it is filiform and exceeds the combined lengths of the egg and the little foot (many Microcotyle ). In certain cases, the filament of the egg forms a small widening at its free end. Among a number of species (for instance among Microcotyle caudata Goto), the little foot of one egg fuses with the filament of another forming, in such a fashion, a little chain of a varying number of eggs. Oftener the feet of individual eggs merge together into a common foot of several eggs (for instance Acanthocotyle). Finally, sometimes the filaments of the eggs can also become agglutinated to each other (certain Microcotyle ). The color of the eggs varies from bright yellow to dark brown. Usually the color changes from a lighter to a darker shade at the time of formation and further development of the egg. Among different species the sizes of the eggs fluctuate from 0. 02 to 0. 18 mm without including the length of the little feet and the fila- ments. The latter may be many times (more than 60) the length of the egg itself. In a number of cases the sizes of the eggs can vary greatly within a single species. Thus, in Dactylogyrus vastator Nybelin we have observed eggs from 0. 074 to 0. 126 mm in length, that is the linear in- crease of size was almost double and the volume even more so. The manner of deposition of eggs of monogenetic trematodes can be divided into two groups, the first deposits eggs into the water and they fall onto the bottom or onto different objects on the bottom; the second produces eggs which attach themselves to the body of the host or be- come stuck in the inucous which surrounds the location of the parasite. To the first group are related forms wherein the little feet and filaments of the eggs are absent or, on the contrary .those which possess powerfully developed offshoots from the eggs but which predominantly deposit eggs in groups or by "portions." Thus, this is the majority of Dactylogyridae, Polystomatidae, Diclybothriidae, and many other fresh water and marine p. 91 species the eggs of which are without offshoots. On the other hand, here also is related the often -mentioned Microcotyle gotoi Yamaguti, According to 90 our observations the eggs of this species, numbering about 75 to 125, form a packet of very long filaments by means of ent'wining, which (the packet, nobis) is deposited all at once and does not delay itself on the gills of the host but falls into the water. In the water it turns upside down with the spool of the filaments down; the eggs comprising it spread fanwise in all directions forming a shape similar to that of a little umbrella or parachute which settles very slowly. The little feet of the eggs point in all directions with their hook-shaped ends and grab the sea plants and prevent the whole group of eggs from settling out of the water. This contrivance undoubtedly is consistent with the conditions of life of the Terpug, Hexagramidae--the host of M. gotoi--so that the emerging larvae will fall into more or less favorable conditions for the infection of the young host (for more details see page 118). As a rule the eggs of the representatives of the second group have more or less well-developed little feet and very often filaments. Often the eggs attach themselves to the body of the host by the little feet, and it is quite probable that they attach themselves not only mechanically by the terminal widening but also glue themselves to it. Usually during this process the maternal individual performs special motions while depositing the eggs which help in the gluing of each egg individually. Thus, the eggs of Nitzschia sturionis (Abildgaard), according to our observations, glue themselves to the mucous membrane of the buccal cavity of sturgeon-type fishes. Even in artificial conditions in a glass container the eggs glue them- selves so strongly that they cannot be torn away by a strong stream of w^ater fronn a pipette. Among species with sharpened feet and filaments, the latter retard themselves on the body of the host by mechanical action. For in- stance, according to our observations of Mazocraes of Caspian herring, during the period of intense egg-laying on the gills of the host there are many hundreds of deposited eggs and they are attached to the gills very strongly in spite of the fact that they do not have any special growths or indentations on the little feet or on the filaments. It is quite probable that the gluing of certain Hexabothriidae in long chains of from 10 to 15 units each, which was observed by Thaer (Thaer, 1850), appears as an adaptation to the easier retention of the eggs on the body of the host. There is reason to believe that the eggs of all monogenetic trematodes have an envelope which is agglutinous to some extent. Study under artificial conditions, however, does not permit us to substantiate this with complete conviction. Embryological development of the egg -laying species has been in- sufficiently studied. For all practical purposes only the development of Polystoma integerrimum Froelich was studied (Goldschmidt 1902a, 1902b; Halkin, 1901). ^ In this species the cleavage is complete and unequal and •'• P. G. Svetlov pointed out to us the existence of one more work (Minouchi, 1936) which was not known to us at the time of the writing of the present section. 91 at the same time irregular. Only in more advanced stages, the gradually- larger blastomeres are grouped in the middle with the smaller ones around and an epibolic gastrula results. Then all the borders of the cells disap- pear and a syncytial mass results inside of which occurs isolation of the rudiments (anlage, nobis) of the tissue's and of the organs of the larvae. One must suppose also that among the remaining egg -laying monogenetic trematodes the embryological development takes place in a similar fashion and consequently the presence of a holoblastic egg of irregular cleavage and epibolic gastrulation is characteristic for this entire group. Annong vivi- parous forms the cleavage was studied by Metschnikoff (Metschnikoff , 1870), Wagener (Wagener, 1860) and Kathariner (Kathariner, 1904). All these p. 92 authors worked on the development of different species of Gyrodactylus. Among the representatives of this genus the cleavage takes place just as irregularly and chaotically as among Polystoma . In the cleavage of the egg of Gyro- dactylus it is characteristic that in the very early stages one large blastomere individualizes itself and later becomes the origin for the embryos (germ) of the following generation. As is known, a very peculiar development is observed among Gyrodactylus during which a number of larvae are formed from a single egg, not at the same time, but gradually one after the other. Gastrulation in Gyrodactylus is just as epibolic as in Polystoma. However, the formation of the syncytial mass does not take place and organogenesis develops by way of differentiation of cellular sections. The entire develop- ment unfolds inside the uterus of the maternal organism and an adult worm is born which does not differ in size from the maternal individual. A pe- culiarity of the development of Gyrodactylus is that during the very early stages, a second embryo forms inside the first embryo, inside of which soon is incepted a third and inside the last sometimes even a fourth. A number of researchers headed by Kathariner who worked specially on this question consider this phenomenon as polyembryonia, and others take it as one of the forms of paedogenesis. In order not to return again to Gyro- dactylus, let us note that the development of the attaching apparatus among the representatives of this genus coincides in basic characters with that of Dactylogyridae (see development of Dactylogyrus , page 139 ). The periods of the development of eggs from the moment of their deposition until the emergence of their free-swinnming larvae are very different species and, as was shown by a number of studied, depend to a large degree upon the temperature of the surrounding medium. Generally one may say that in normal temperature conditions (obviously varying among the different species) the development lasts from 3 to 35 days; however, these periods can be considerably altered artifically; (for periods of develop- ment of the separate species see the "Appendix, " pages 13 to 216). Thus, according to the data of Lyman (1951a), at the temperature of 4 degrees C the development of the eggs of Dactylogyrus vastator Nybelin does not take place at all. At a temperature of 8 degrees the larvae of D. vastator emerge from the shell of the egg on the 27th or 28th day, at 12 degrees --10th to 11th day, 16 degrees --6th to 7th day, 20 degrees --on the 5th day, 24 degrees --4th day. 92 and 28 degrees --3rd day. In our opinion, these numbers are close to the truth but understandably err by excessive precision and definiteness. Actually, the process of development of larvae undoubtedly fluctuates con- siderably at the same temperature and conversely the period of develop- ment can be the same under fairly strong fluctuations of the temperature (Bychowsky, 1933). The larvae emerge from the eggs through an aperture which is formed on the upper end of the egg after the falling away of the operculum. The latter is opened due to the slight jars of the larva which is lying in the egg and sometimes only after considerable effort on its part, in a number of cases during the course of two to three hours. Very often, in normal conditions we happened to observe the deaths of larvae of the latter because of the impossibility of opening the egg due to the fact that it was overgrown by certain vegetable or bacterial organisms. As a rule, the little larva formed in the egg normally lies with the head end toward the operculum of the egg. In rare cases we observed the formation of little larvae lying the other way around, and these larvae in a majority of cases were unable to turn around and come out of the egg. The emergence of the larvae usually takes place during the warmer time of the twenty-four - hour period, predominantly in its first half, and with the lowering of temperature it is possible to retard the emergence of fully formed larvae for several days. Undoubtedly the illumination of the latter exercises considerable p. 93 influence on the emergence of the larvae from the eggs, thus it was possible for us to delay for rather long periods the emergence of the larvae among a number of species of Axine by placing the eggs in a dark place. And we were able to regulate the emergence of formed larvae precisely enough by sw^itch- ing them to a lighted place. The larvae which emerge from the eggs move at first almost in straight lines, now accelerating, now delaying their motion. During the time of this first period of their life the larvae are characterized on the one hand by a strongly expressed positive phototropism; on the other hand by the inactive condition of the attaching apparatus because of which they cannot attach themselves to the body of their host. Both these peculiarities repre- sent an important adaptation to the creation of the best conditions of dissemi- nation of the larvae in the water. This period is succeeded after a certain interval by another, and is characterized by the fact that the larvae acquire ability for attachment and that among them the positive phototropism dis- appears or at least is strongly reduced and, for the most part, . the negative phototropism is acquired. During this time, which is the longest in the larval period, the larva swims with undiminished speed but quickly changes 1 The negative phototropism of the larvae of Diplorchis ranae Ozaki in- dicated by Ozaki (Ozaki, 1935b) is undoubtedly related to the following (second, nobis ) period of the life of the larvae. 93 its direction, often stopping and bumping against different objects as if feeling thena with its anterior end and often attempts to attach itself by its posterior end. When it finds a host the larva passively or actively penetrates to its place of habitation, attaches itself and, casting away its ciliary cover- ings, begins its parasitic life. However, when it fails to find its host the larva does not perish at once but still swinns for a long time although it already does not move its attaching disc and its armature, having lost the ability to attach. In such a fashion, we can distinguish two periods in the normal life of the larvae with different physiological characteristics which can be distinguished morphologically at the same time by the condition of the attach- ing disc. During the first period, the latter carries its chitinous armature inside the body and only after it "cuts itself" outside and the sharp ends of the hooks penetrate or protrude and begin to move actively does the larva acquire the ability to attach itself to the body of the host. It is precisely the moment of the "emergence" of the hooks that determines the change of the larva from the first period to the second period. The time of the pre- sence of the larvae in the first period varies. For the majority of Dactylo- gyrus it is equivalent to two to three minutes or even shorter, whereas for Nitzschia sturionis (Abildgaard)--not less than five minutes and in most cases longer (from 10 to 12 minutes). Then the second, most important period is considerably longer. Thus, for Dactylogyrus it is not less than 4 to 5 hours and for Nitzschia about 24 hours. The biological significance of the two periods of life of the larva is very great. Actually the ability of the larva to swim actively is an adap- tation for the dissemination of the species to different individuals of its host. If the larva had the ability to attach itself immediately to the body of its host the infestation of the individual of the parent host on which the egg was developed would have increased to a considerably greater degree than the infection of other individuals, which undoubtedly would not have been advan- tageous fronn the point of view of dissemination and consequently from the point of view of the flourishing and preservation of the species. The ex- p. 94 istence of the first period of life of the larvae appears to be a supplementary special adaptation which prevents increased infection of the same host indi- vidual. Indeed, both the increased activity of the larva and its positive photo- tropismplus its inability to attach- -all these do not allow it to remain on the same host individual but force it to seek another. The above-mentioned adaptations undoubtedly play a greater role among worms, the eggs of which remain on the host, than among those which deposit eggs on the bottom. Postembryonic developnnent of the egg -laying monogenetic tre- matodes has been studied somewhat better than the embryonic, but is also insufficiently known. Basically, at our disposal there are data about the structure of the newly emerged larvae and only to a small degree do we 94 know about the nature of the further development up to the time of maturity. At the present time, literary data concerning the development of 13 genera and 22 species are known to us, ^ namely: 1) Acolpenteron 1 ~~~ References to authors who conducted experiments are reproduced in the appendix (pages 138 to 216 ). Data fronn the published works of our labo- ratory are not included in the present list. catostomi Fischthal and Allison, 2) Dactylogyrus vastator Nybelin, 3) D, anchoratus (Dujardin), 4) D. crassus Kulwiec, 5) D. formosus, Kulwiec, 6) D. wegeneri Kulwiec, 7) D. macracanthus Wegener, 8) Ancylodiscoides vistulensis Siwak, 9) Benedenia melleni (MacCallum), 10) Polystoma integerrimum Froelich, 11) Polystoma nearcticum (Paul), 12) Polystomo- ides oris Paul, 13) Diplorchis ranae Ozaki, 14) D. scaphiopi Rodgers, 15) Sphyranura oligorchis Alvey, 16) Octostoma scombrii Beneden and Hesse, 17) Diclidophora luscae (Beneden and Hesse), 18) D. poUachii (Beneden and Hesse), 19) Diplozoon paradoxum Nordmann, 20) Microcotyle spinicirrus MacCallum, 21) M. donavini Beneden and Hesse, 22) Diplasiocotyle johnstoni Sanders. From 1928 to the present time, 24 genera and 62 species were studied for the first time and checked for the verification of the data of previous researchers by us and by our collaborators. ^ Those which were studied by us personally are noted by asterisks. *1. Dactylogyrus vastator Nybelin 17. *2. D. anchoratus (Dujardin) 18. *3. D. solidus Achmerow 19. *4. D. formosus Kulwiec 20. *5. K. wegeneri Kulwiec 21. *6. D. intermedius Wegener 22. *7. D. cornu (Linstow) *23. *8. D^ fallax Wegener *24. *9. D. crucifer Wagener *10. D. longipula Bychowsky *25. *11._D. varicorhini Bychowsky *26. *12, D. pulcher Bychowsky *13. D. modestus Bychowsky 27. 14. D. curvicirrus Achmerow 28. 15. D. gussevi Achmerow 16. D. phoxini Malewizkaja 29. D. erythroculteris Gussew D. achmerowianus Gussew D. obscurus Gussew D. contortus Gussew D, leucisculus Gussew D. peltatus Gussew Dogielius planus Bychowsky Ancyrocephalus paradoxus Creplin A, (s. la£. ) cruciatus (Wedl). A. (s. lat. ) vanbenedeni (Parona and Perugia) A. (s. lat. ) pavlovskyi Gussew A. (s. lat . ) morgurndae Yannaguti A. (s. lat. ) curtus Gussew 95 30. A. (g. lat. ) hemibarbi Achmerow *47. *31. Protancyrocephalus strelkowi Bychowsky *48. *32. Ancylodiscoides siluri (Zandt) 49. *33. A. vistulensis (Siwak) 34. A. various Achmerow *50. 35. A, strelkowi Achmerow 36. Bychowskyella pseudobagri *51. Achmerow *52. *37. Diplectanum aculeatum Parona and Perugia *53. *38. D. similis B ychowsky *39. Heteroncholeidus buschkieli *54. Bychowsky *55. *40. Lamellodiscus elegans Bychowsky *56. *41. L. fraternus Bychowsky 57. *42. Calceostomella inerme *58. (Parona and Perugia) *59. *43. Tetraonchus monenteron 60. (Wagener) *6l. *44. Tetraonchoides paradoxus *62. Bychowsky *45. Nitzschia sturionis (Abild- gaard). *46. Benedenia derzhavini (Lajman) Polystoma integerrimum Froelich P. ozaki Price Neopoly stoma palpebrae Strelkow Diclybothrium armatum Leuckart Mazocraes alosae Hermann Qctostoma scombri, Beneden and Hesse Diclidophora denticulata (Olsson) Discocotyle sagittata (Leuckart) Diplozoon paradoxum Nord- mann Microcotyle mugilis Vogt M. pomatomi Goto M. gotoi Yamaguti M. sebastis Goto Axine belones Abildgaard Axine sp. I Axine sp. II p. 95 Altogether , in this fashion we dispose of the data about the development of 29 genera (75 species) related to the following 13 families: Dactylogyridae (Dactylogyrinae--Acolpenteron Fischthal and Allison, Dactylogyrus Diesing, Dogielius Bychowsky; Ancyrocephalinae- -Ancyro- cephalus Creplin, Protancyrocephalus Bychowsky, Ancylodiscoides Yama- guti, By chowskiella Achmerow, Heteronchocleidus Bychowsky), Diplectanidae (Diplectanum Diesing, Lamellodiscus Johnston and Tiegs), Calceostomatidae ( Calceostomella Beneden), Tetraonchidae ( Tetraonchus Diesing), Tetra- onchoididae (Tetraonchoides Bychowsky), Capsalidae (Benedeniinae-- Benedenia Diesing, Nltzschiinae Nitzschia Baer), Polys torn atidae (Polystoma ) Zeder, Polystomoides Ward, Neopolystoma Price , Diplorchis Ozaki), Sphyra- nuridae (Sphyranura Wright and MacCallum), Diclybothridae ( Diclybothrium Leuckart), Mazocraeidae (Mazocraes Hermann, Qctostoma Otto) Diclido- phoridae ( Diclidophora Diesing), Discocotylidae ( Discocotyle Diesing, Diplozoon Nordmann), Microcotylidae (Microcotyle Beneden and Hesse, Axine Abildgaard, Diplasiocotyle Sanders). -^iC^^ 96 Fifteen families reinain unstudied- -Protogyrodactylidae, Monocotylidae , Loimoidae, Dionchidae, Microbothriidae, Acanthocotylidae, Amphibdellatidae , Bothitrematidae , Hexabothriidae , Chimaericolidae, Hexostomatidae , Anthocotylidae , Plectanocotylidae, Protomicrocotylidae, and Gastrocotylidae. The study of representatives of these families is a problenn of first priority and above all Microbothriidae, Bothitrematidae, Hexabothriidae and Hexostomatidae should be studied because their location in the system is doubtful and information about larval stages must play a deciding role in the final elucidation of this question. Because the number of unstudied families is larger than those studied, it appears at first sight that it is premature to make generalizing conclusions; however, this is not true, inasmuch as we can also judge the structure of the larvae in the majority of the unstudied families from the existing data. We cannot expect principal differences among the larvae of Protogyrodactylidae and Dactylogyridae,and (judging by, nobis) the structure of the adults we can say with great accuracy what the larvae must be in this aberrant family. The same can be said about Monocotylidae, Loimoidae and Dionchidae, the larvae of which must be very close to those of Capsalidae, The structure of the larvae of Acanthocotylidae is clear, because the adult individuals have an unchanged larval disc. The larvae of Amphibdellatidae and Tetraonchidae are undoubtedly very close. There are no special doubts^ either about the larvae of Anthocotylidae, Plectanocotylidae, Protomicro- cotylidae, or Gastrocotylidae because the structure of the adult indi- viduals provides the basis for a sufficiently precise idea about the nature of their larvae. In such a fashion the material which exists on the subject of the development of the 13 families gives fully sufficient data for the general representation about the larval stages of the overwhelming majority of Monogenoidea. It is understandable that separate details of the structure p. 96 remain unknown, but this concerns mainly the secondary peculiarities from the point of view of the analysis of the phylogeny of the group. All the data on the subject of the development of separate species are placed by us into a separate appendix (pages 138 to 216 ) to which we refer those who are interested. Here is expressed only generalized material about the character and peculiarities of the postembryonic period and the development of monogenetic trematodes. The presence of the free -swimming larva equipped with a c iliated covering is characteristic for all Monogenoidea. Representatives of Gyrodactylidae appear as exceptions, inasmuch as they are viviparous. We consider the data of Alvey (Alvey, 1936) about the absence of the ciliated coverings among free-swimming larvae of Sphyranura oligorchis Alvey as erroneous (see page 192). 97 Basically the larvae of all monogenetic trematodes are charac- terized by the following signs; first, the presence of a ciliated covering, located mainly in three zones --near the head end, in the middle of the body, and near the attaching disc; second, by the presence of head glands the efferent ducts of which are grouped by bunches opening outside in the anterior head lobe of the body; third, the presence of strongly differentiated systems of internal organs --of the digestive system with the pharynx and intestine developed to a certain degree, with the excretory system with basic ducts and a number of protonephridial cells and a nervous system with isolated head ganglia and longitudinal nerve trunks and one to two or four eyes (a number of exceptions); fourth, powerfully developed attaching discs always equipped with chitinous armature consisting of a certain number of varying or similar hooks. One can expect that the enumerated characters probably were also characteristic for the primary larvae of monogenetic trematodes and it appears to us that in addition, one should consider the location of the buccal aperture on the ventral surface much closer to the middle of the length of the body than is observed among contemporary species, as very probable, for we see that the buccal operture is located closer to the midole of the body among larvae of more primitive contemporary Monogenoidea than among the more highly organized ones. The nature of the ciliary covering of contempo- rary species does not allow us to speak with certainty concerning the direction of its evolution, but nevertheless it is probable that initial forms possessed a continuous ciliary covering and its division into separate zones is a secondary phenomenon. Further, it is completely clear that hooks were the initial armature of the ancestors of monogenetic trematodes and not suckers or clamps which, just as in the individual development, histori- cally appeared later. In all probability among the ancestral species the chitinous armature of the attaching disc was represented by a great nunnber of hooks equal in form and size and lying along the edges of the posterior end of the body which was not yet differentiated into the fornn of a disc (which was, nobis ) apparently already somewhat flattened, as we observe among a number of Rhabdocoela. A clearly expressed tendency toward the decrease in the number of edge hooks in proportion to their morphological complication among contennporary monogenetic trematodes serves as a basis for these suppositions. Such a larva (Fig. 114) of monogenetic trema- todes does not differ in principal from the adult form which develops from it. Basically the differences can be reduced to the appearance and develop- ment of the sex system and the progressive growth of the organs of all systems. Concerning the sex system, we can maintain that it was incepted p. 97 and developed in the posterior half of the body behind the end of the intestinal system. Finally, it is not less probable that the ciliary covering of the larvae remained during their attachnnent to the host in the beginning as this happens in a number of ectoparasitic Turbellaria. Having thus recreated in considerable measure a promonogenetic trematode (Fig. 115), we see that its similarity with the Turbellaria is so great that we could, without any 98 hesitation place such a form in the same group as Rhabdocoela, which agrees with the commonly accepted view of the origin of monogenetic trema- todes. The development of the chltinous armament of the posterior end of the body, which assume the function of attachment at the expense of a decrease in the role of the adhesive glands attaching to the substratum, which are so charac- teristic of Turbellaria, can, by themselves, serve as the basic character indicating the formation of tlie new group. We can clearly divide the larvae of monogenetic trematodes into two basic groups differing by a number of charac- ters and at the same time charac- teristic for two morphologically ..N\\\\\\ ///-■■//. p. 98 Fig. 114. Hypothetical free -swimming larva of promonogenetic trematodes. Explanation in text. Fig, 115. Hypothetical promono- genetic trematodes. Explanation in text. different groups of adult Monogenoidea. To the first group are related the larvae of eight families— Dactylogyridae, Diplectanidae, Calceostomatidae , Tetraonchidae, Tetraonchoididae, Capsalidae, Polystomatidae, Sphyranuridae. And to the second,the remaining five --Mazocraeidae, Diclidophoridae, Discocotylidae, Microcotylidae, and Diclybothriidae, The last family, however, has a number of distinctive traits which place it somewhat in isolation (see further page 404 ). 99 A typical larva of the first group has the following structure (Fig. 116). Its body is elongated and cigar-shaped, and it is provided with three zones of ciliary epithelium. There are well-developed head glands which open outside by two groups of ducts on the anterior edge of the head end. The anterior end of the body has'two pairs of well-developed pigmented little eyes with light refracting lenses. The buccal aperture is located ventrally at the level of the first pair of eyes or even in front of it. The pharynx is powerfully developed, the intestine is circular. There is a weakly developed nervous system and excretory system. The sex system is not developed but for the most part a group of large cells representing p. 99 Fig. 116. Free -swimming larva of the first type. Explanation in text. Fig. 117. Free-swimming larva of the first type. Explanation in text. the sex embryo (gonad anlage, nobis ) lies inward from the intestinal ring. The attaching structure of the posterior end of the body consists of 14 to 16 edge hooks. They have a well-developed terminal little hook and a more or less well-developed handle. The latter is firm, hard and not flexible. Its growth (if it takes place in the postembryonic period) takes place at the expense of a super growth (accretion, nobis) at the free end (skeleton-forming cells lie near the upper end of the handle. ) 100 The larvae of the second group (Fig. 117) have a similar body shape and are also equipped with a ciliary covering which is divided into three zones, but which for the most part is more powerfully developed. There are also well -developed glands of the head end opening outside for the most part by three groups of ducts. Usually, the eyes are in the number of one fused from two (which is clearly indicated by the pre- sence of two light refracting lenses), more seldom there are two eyes and even more seldom- -four (Diclybothrium, Axine). The buccal opening is somewhat closer to the anterior end than among the larvae of the first type. The pharynx is powerfully developed and is located at a greater distance from the buccal opening, the intestines are circular or sac- shaped, A development of the nervous system and. excretory system is approximately the same as in the first group. The sex system is incepted behind the intestinal sac or in the same fashion as among the larvae of the first group. The attaching armature of the disc consists often to twelve edge hooks or, as an exception, of a smaller number (genus Diplasiocotyle), or the edge hooks can even be absent, but then there are other attaching formations (genus Diplozoon). As a rule the edge hooks of this group are already fully developed during the period of embryonic development and differ from the edge hooks of the larvae of the first group in that their little hook is more elongated, whereas the handle is straight or slightly curved, more delicate and flexible. Within the limits of the group of the larvae of the first type we observe differences in the attaching apparatus which have quite regular character. On the one hand, they concern the chitinous armature of the disc, and on the other hand, the appearance of attaching formations supplementary to it- -suckers. As was pointed out earlier for the families of Monogenoidea which have similar larvae, the attachment of adult forms takes place either only with the help of chitinous armature or with the help of the disc --sucker, or with the help of suckers on the attaching disc. It is understood, that be- tween these methods of attachment there are a number of transitions when the worms attach" utilizing different formations at the same time. The most primitive undoubtedly appears to be the attachment with the help of the chitinous armature (alone, nobis) and the most complex for a given group- - suckers. The change in the structure of the attaching apparatus of the larvae develops in the same direction as the adaptation to the attachment among adult forms. The larvae of Dactylogyridae , Diplectanidae, and Tetraonchidae possess only chitinous armature, and the adult forms of this family also attach only with its help. The larvae of Calceostomatidae and Capsalidae possess only chitinous armature also, but their adult forms maintain themselves on the host mainly by means of a disc transformed into a sucker. Tetraonchidae and Tetraonchoididae, which have a larva similar to the more simply or- ganized Dactylogyridae, probably attach themselves with the help of a disc and partially by chitinous armature. The larvae of Sphyranuridae attach themselves with the help of chitinous hooks and suckers in the same fashion as their adult forms. F inally, in the adult condition, Polystomatidae attach 101 themselves only by suckers, whereas the larvae have only the chitinous armature. At first glance there appears alnnost no correlation in the p. 100 structure of the attaching apparatus of the larvae and in the adults; how- ever, it is far from that. The edge hooks of the larva which have just emerged from the eggs of the more simply organized monogenetic trematodes have not yet reached their final sizes and shapes, whereas among highly organized representatives they acquire their permanent sizes and shapes in the embryonic period. Similarly, we observe that edge hooks of the first (group, nobis) reach relatively larger sizes than those of the second. At the same time with this, the lowly organized forms have a more complexly arranged handle of the edge hooks which annong them is often differentiated into a number of divisions well -delineated from each other. Finally, very often separate pairs of edge hooks are distinguished from each other by size which happens only in exceptional cases among highly organized mono- genetic trematodes of this group. Along with the changes of edge hooks, we observe the appearance of middle hooks, which also have a regular character. Among the more lowly organized groups they are absent from the free-swimming larvae and also among adult fornns (the absence of middle hooks appears as a secondary phenomenon among highly organized specie^. Later, middle hooks appear, at first- -after the embryonic period, and then during it in such a way that the inception of the hooks takes place successively during more or less early stages, and finally - entirely in the egg. The free -swimming larvae grow a successive number of middle hooks from one pair to three as is the case among adult forms. Just as in the edge hooks, one can note that the relative tempo of the growth of the middle hooks decreases with the increase in the organization of the adult animal. Finally anmong those specieswhich have been studied, the larva of Sphyranura oligorchis already has one pair of suckers in addition to the chitinous armature aa it emerges from the egg, just as the adult form. The growth of the middle hooks and suckers of Sphyranura continues even later. The second group of larvae demonstrates basically the same normal complications of the attaching apparatus. Among the adult animals related to it, attachnnent by means of clamps or the presence of sucker-shaped clamps is characteristic, as among Diclybothriidae and Diclidophoridae. Their number varies greatly within limits of the entire group, but the general tendency goes toward the increase of their number from four pairs to several tens or even hundreds. The larvae emerging from the egg have chitinous arnnature of the hook type and some more highly organized forms also have clamps. Among Mazocraeidae and Diclidophoridae, the free- swimming larvae have five pairs of edge hooka, Discocotylidae have three pairs of edge hooks (among Diplozoon paradoxum they are absent), one pair of middle hooks and one pair of attaching clamps. Microcotylidae usually have five pairs of edge hooks and two pairs of middle hooks [among Microcotyle spinicirrus MacCallum, six (?) pairs of edge hooks 102 and among Diplasiocotyle johnstoni Sand, three pairs of edge hooks and finally Microcotyle mugilis Vogt has, besides edge and middle hooks, still one more pair of attaching clamps] , Diclybothriidae, five pairs of edge hooks and two pairs of middle hooks. For representatives of these groups it is characteristic that all hooks, the lateral as well as the middle, do not grow at all during the postembryonic period. As a rule they are either retained unchanged during the entire life or are replaced by a clamp or are even discarded from the body of the animal (see page212 ). The excep- tion is represented by Mazocraeidae among which, during the postembryonic period, there appears still one more pair of middle hooks which (and only p. 101 they) grow for a sufficiently long period and considerably, and Diclybothriidae among which the relationships are somewhat more complicated (see further). Within the limits of this group we see certain tendencies toward the decrease in the number of edge hooks among specialized species(Discocotyle , Diplozoon, Dipliasiocotyle) . Finally it is extremely curious that the attaching clamps of the first four pairs are incepted on the bases of the edge hooks, which apparently enter into the composition of the chitinous parts of the clamps to some degree. Among monogenetic trematodes which have more than four pairs of clamps, all incepted after the first eight are formed without the participation of edge hooks, and by this they differ principally from the preceding ones. V. A. Dogiel (1954) writes on the subject: "From here we can make the following essential conclusion: in the first place all the anterior clamps of Microcotylidae have a different origin than the four posterior(pairs , --B,B. ) and because of that are not homologous to them: in the second place, because of what has just been mentioned, the formation of numerous anterior clamps must be considered not as polymerization (that is the multiplication of a number of homologous organs) but as a numerous (plural, nobis) inception of new organs not homologous to the posterior -- four (pairs, -- B.B. ) clamps. " Subsequently, the «_lamps of the larvae which have relatively very small sizes grow considerably. Their growth differs significantly from the growth of the hooks because all the parts of the clamps are incepted at once, but in small sizes, and after that they grow equally in all their parts. A few words about middle hooks in the larvae of this group. Middle hooks of the larvae of Mazocraeidae, Discocotylidae , Diclidophoridae , and the first pair of middle hooks of the larvae of Microcotylidae generally strongly resemble the edge hooks in their shapes and differ nnainly in their somewhat larger sizes. It seems to us that, taking into consideration their appearance in the embryonic period at the same time with the edge hooks and also the places of their inception, it is more correct to consider them as the sixth (more precisely the first ) pair of edge hooks; whereas the second pair of middle hooks, which is incepted in the embryonic period among Micro- cotylidae and in the postembryonic period among Mazocraeidae, clearly differs in structure and is not equivalent to edge hooks. 103 As was already indicated, the larva of Diclybothriidae (Fig. 221) appears somewhat different from the other larvae of this group; it has, in addition to the typical five pairs of edge hooks, two pairs of middle hooks and the latter are of strange shape not resembling any of the middle hooks of other species which have been studied. In our connmon work with A. V. Gussew (Bychowsky and Gussew, 1950) we wrote: "Homology of the chitinous hooks of the larvae with the ones of the adult animals does not occasion ajiy doubt. The anterior three pairs of edge hooks correspond to the hooks of the suckers--clamps, the fourth pair--to the third pair of hooks of the narrowed part of the disc, the fifth pair corresponds to the small hooks of the posterior end and in this fashion it is the only one of them all which is not subjected to any noticeable change in sizes and form. The first and second pairs of middle hooks of the larvae correspond to the ones of the narrowed part of the disc of the adult individual. It is curious to note that the latter hooks and the second pair of middle hooks of the larvae, which strongly differ in shape acquire considerable similarity during further develop- ment. One must note this circumstance in light of the evaluation of the inter- relationships of the chitinous formations of the adult individuals for the building of phylogenetic links within the limits of the group. " From what has been said, one must consider that in comparing the chitinous armature of Diclybothriidae with the one of Microcotylidae , the first pair of middle hooks p. 102 of the latter corresponds to the second pair of the fornner and conversely the second pair, that is actually the middle hooks of Microcotylidae, correspond to the first pair of the hooks of Diclybothriidae. At first glance the presence of two pairs of pigmented eyea, which are not observed among all other larvae of the second type, appears to be a basic difference between the larvae of Diclybothriunn and the other larvae of this second group as well as the majority of the larvae of the first type. However, we have often indicated that within the limits of the most diversified group of Monogenoidea there exists a tendency toward the reduction of (the size of, nobis) eyes and of their number. Taking into consideration also that within the limits of one family eyes can be either present or absent among closely related types, this circumstance cannot have serious phylo- genetic significance. This is substantiated by the very convincing data on the embryology of Axine which appears to be a typical Oligonchoinea. The larvae of this genus which were examined have four eyes and it is essential that among Axine sp. I both pairs are normally developed, among Axine sp. II the anterior pair fuses and the second is normally developed and relatively larger whereas, among A. belones Abildgaard, the anterior pair is fused while the posterior is very weakly expressed. There is clearly a tendency toward the disappearance of the second pair of eyes and the preservation of one fused eye, which is characteristic for typical Oligonchoinea (see page 214 ). 104 In such a way, returning to Diclybothriidae, it seems clear that their larvae belong in the category of the second type despite some differ- ences, just as the family itself stands within the limits of Oligonchoinea (see page 402 ). As a peculiarity of the family connected with the morphology of the adult forms appears the fact that, as has been pointed out, all chitinous elements, with the exception of the fifth pair of edge hooks, grow intensely during the first embryonic period. Apparently the family of Hexabothriidae (see page405 ), which was studied by us, has the same peculiarities. The subsequent development of the larvae of both types proceeds with a varying degree of speed according to the degree of complication of the attaching apparatus, on the one hand, and of the progressive development of all systems of internal organs on the other hand. The complication of the attaching apparatus from the larval stage to the one possessed by the adult forms is observed in the following directions: 1) intensified development of the chitinous attaching apparatus of the hook type; 2) intensified development of the attaching disc itself as an organ of attachment; 3) the development of the suckers or attaching clamps on the attaching disc in the process of development; 4) the appearance of new disc -shaped organs of attachment not homologous to the initial (or primary, nobis) attaching disc. The development of the hooked chitinous apparatus proceeds along the line of complication and differentiation of edge and middle hooks and the appearance of supplementary chitinous formations supporting the hook apparatus and coordinating its work. The edge hooks of the more primitive Monogenoidea have the same shapes in all stages of life and grow synchronously with constant speed. Among more highly -organized species the process develops along two lines --on the one hand deviation in sizes of different pairs of edge hooks often accompanied by a change in shape takes place, and on the other hand the changes proceed along the line of preservation of the initial sizes of the hooks and a gradual loss of their significance with the increasing role of the middle hooks. The latter have, as was indicated earlier, varying shapes and sizes and a tendency toward the p. 103 increase of the number from one to two or even three., pairs. In connection with the complication in the structure of the hooks and their more powerful development, connecting plates of different types which were already mentioned (see page28 ) usually appear. As a rule, these connecting plates are developed more powerfully in forms having a larger disc and more powerful armature. In an original form of Heteronchocleidus buschkieli Bychowsky (see page 164 and Fig. 118) the adult worms have three powerfully developed middle hooks, the fourth remains undeveloped and the two connecting plates which appear are located in such a way as to serve for the connection of all three hooks into one coordinate system. Among many Dlplectaninae the three con- necting plates (Fig. 56) lie in such a way that on the one hand they support the disc in the completely unfolded shape, and on the other hand, they are connected with the four middle hooks so that the latter, lying in pairs, play the role of two attached, pincer -shaped systems and not four independent formations. 105 In a number of groups the role of the chitinous hook armature decreases in proportion to the growth of the animals and the powerfully developed disc acquires the main significance. It transforms into a sucker similar to that of leeches or digenetic trematodes. During this process the edge hooks do not grow as a rule but retain their initial sizes while the middle hooks remain without change, losing their signficance (Calceo- stomatidae), or continue to grow, partially preserving the attaching role and become mainly a supporting apparatus (Nitzschiinae and others). Characteristic for Polystomatidae is the fact that the chitinous armature is preserved during the appearance in the postembryonic period of suckers on the attaching disc (the latter also increases strongly, ^ and the Cases of its disappearance, although it may be partial, are known. middle hooks grow and for a cer- tain time still function, whereas the edge hooks remain partially on the posterior and anterior edges of the disc and partially in the centers of the developing suckers (one in each sucker) without changing sizes, but cease to function completely. Among species in which attaching clamps develop in the disc, the fate of the chitinous larval arnniature differs, but generally it doesn't grow (exception, Diclybo- thriidae, see above) and is not fully preserved. For the most part the edge hooks enter into the composition of the clamps which are in the process of formation p and thus they disappear and one pair is either preserved for the entire life of the worms without change or is cast off completely. One pair of middle hooks that apparently represents modified edge hooks with changed shapes, as a rule does not grow (just as for edge hooks the exception is Diclybothriidae), whereas in a number of cases the second pair grows (Mazocraeidae) and in others remains without changes (Microcotylidae). In a number of Microcotylidae both pairs of middle hooks and one pair of the edge hooks, which was already indicated, usually lie in common in a small narrowed section of Fig. 118. Heteronchocleidus buschkieli Bychowsky, adult worm from the gills of little aquarium fish Macropodus opercularis (L. ) Leningrad. 104 106 the posterior end of the attaching disc and they fall off during the early stages of postembryonic development together with this portion of the body. Finally, during the period of postembryonic development, cer- tain species (Diplectanum) form special disc-shaped growths on the ventral and dorsal sides of the anterior part of the attaching disc and these growths are equipped with chitinous stick-shaped plates or chitinous rings which serve as auxiliary organs of attachment. Analogously to this, apparently, a secondary attaching disc is formed in Acanthocotylidae among which the primary disc loses its attaching signficance soon after the emergence of the larva from the egg, although it is preserved during the entire life of the worms. During the time of the postembryonic period the development of internal organs takes place with different speed among various types, and what is most interesting is that very often the individual in the process of development, which has not yet reached its final form and in which a number of parts of the attaching apparatus are still undeveloped, already be- gins to produce eggs which are fully capable of further development. This is observed especially frequently annong representatives of the genus Dactylogyrus. Interesting contrary data on postembryonic development of Dactylogyrus vastator Nybelin were obtained by N. A. Izumova. According to her materials, a fully developed copulatory apparatus appears after 3 to 5 days in the larvae which settle on the gills of the host ( and at the same time also the attaching armature of the disc appears to be fully formed). However, the sex system of D. vastator is fully formed only on approximately the tenth day, and from that time the worms begin to produce eggs. Izumova succeeded in showing that the temperature of the surrounding medium has great influence on the development of the sex system and also on the attaching armature. Thus the larvae, the development of which took place in a temper- ature of 12to 15 degrees, showed gradual change into the mature state. The copulatory organ and attaching armatures reached full development only in the fifth and sixth day. At a temperature of 18to 22 degrees the character of the development of chitinous elements differed considerably. Thus, separate elements of the attaching armature were completely formed much earlier -- 2 to 3 days; just as the copulatory apparatus was formed at this period although, just as during the development under lower temperatures, the mature stage occurred not earlier than 7 days and in this fashion the process of spermato- genesis and oogenesis fell behind the development of chitinous parts. In conclusion one must note, however, that there are almost no observations in our materials nor in the literature concerning the periods of postembryonic development, which understandably exceedingly complicates the comparison of existing data. Separate information on this question is given by us in the "Appendix" (page 138). 107 CHAPTER IV LIFE CYCLES OF MONOGENETIC TREMATODES Studies of the life cycles of parasitic animals are of great inter- p. 105 est from the practical as well as the theoretical point of view. A precise knowledge of the life cycles gives into the hands of the specialists who are conducting a struggle with parasitic diseases the possibility of active inter- ference with the course of the cycle during the periods which are suscepti- I ble to human countermeasures so as to disrupt the further normal course of life of the parasite and by this very action to eliminate any parasitic infection. The works on preservation of man from infection by Dracunculus medinensis in Central Asia serve as an outstanding example of this. | The theoretical significance of the study of the life cycles is not less important. Their knowledge opens the way to the origin and the processes of the establishment of parasitism and gives us understanding of the reasons for the nature of various parasites and also shows the role of historical factors in the function of interrelations between the parasite and the host. On the basis of the analysis of the life cycle of the parasite, we can ascertain the degree of the inherited fixation in its relations with the host, the role of factors of the external medium in relation to the parasite and the host, and the role of the host as an element of the medium of the parasite. All this taken together provides considerable material for the understanding of the evolutionary processes and thus is of general biological significance. ' i Before speaking about life cycles of monogenetic trematodes^ we ' must also indicate what meaning we attach to this definition. A life cycle is i a very complex pnenomenon. It should not be considered apart from the relations j between the animals and the medium in a simplified manner, as is customarily done ' when it denotes a period (extending, nobis ) from the deposition of the egg by the mater- nal individual to the formation of the egg by the filial individual or that offspring which is equivalent to the maternal (stage, nobis) which is formed after a certain number of intermediate morphologically or ecologically distinctive phases. Into the i understanding of the life cycles, in our opinion, must enter all phenomena which take place in the complex parasite-host-surrounding mediunn, from the for- mation of the egg of the maternal individual until the death of the progeny from this egg, including all stages of development of the daughter individual as well as the generations issuing from her but not equivalent to her morphologically. j Within the life cycle, understood in this fashion, we differentiate the sex cycle connected with the reproduction and limited by the time from one period of reproduction to the other, the yearly cycle in which enter all the processes which take place during the year, and the cycle of development which connprises the above-mentioned period extending from the deposition of eggs until the formation of the individual which is equivalent to the maternal one. I 108 The life cycles of monogenetic trematodes have been almost unstudied. There are data concerning the life cycles and the sex cycles of several representatives of the genus Dactylogyrus in the literature (Nybelin, 1925; Wilde, 1937; Groben, 1940; Lyman, 1951b; Bauer, p. 106 1954; and others), Polystoma integerrimum (Zeller, 1872a, 1876; Gallien, 1934c, 1935), Diplozoon paradoxum (Zeller, 1872b), Benedenia melleni (Jahn and Kahn, 1932), Microcotyle spinicirrus (Remley, 1942) and certain others (see chapter on development and the appendix thereto, pages 138 to 216). Along with these materials, which are far from complete, data about separate phases of the life cycles of various fresh water and marine Monogenoidea are scattered in numerous systematic works. Thus, this important question has not been subjected to serious specialized research until the present time. Our material is not exhaustive either, but neverthe- less it furnishes a great deal (of information, nobis) for the understanding of the life cycles of monogenetic trematodes and contradicts the usual notions concerning their extreme simplicity. When it becomes necessary to examine fishes on nnonogenetic trematodes (sic) of ciny body of water (when it becomes necessary to examine the monogenetic trematodes of fishes from any body of water Hobis) , especially marine, many instances provoke perplexity. First of all, in an overwhelming majority of the cases we find that only adult parasites, predominantly of the same age group, are encountered on these fishes, whereas different stages in development and the young worms either are encountered not at all or extremely rarely. Furthermore, what seems incomprehensible is the fact, as was mentioned earlier (see page 78 ), that very frequently thewornns are encountered in 100 per cent of the cases in one age category of the host, but are absent in other (age categories of the same host, nobis). Still greater perplexity results from questions which arise from the study of certain pelagic fishes, as for instance the mackerel of the Black Sea. The eggs of monogenetic trematodes which parasitize this fish are deposited on the bottom. If one considers the conditions (of the bottom, nobis ) of the Black Sea, one wonders how fishes can be infected 100 per cent when the hydrogen sulfide zone prevents eggs which fall to the bottom from developing. All these phenomena and many others which appear during the study of the distribution of monogenetic trematodes in nature are clearly a reflection of the peculiarities of the life cycles and not a chance or accident connected with the shortcomings of the research. To have a correct approach to the understanding of the life cycle of monogenetic trematodes one must, first of all, clearly understand some of the biological groups. As has already been pointed out, Monogenoidea can be divided into two groups according to the method of reproduction, that is into a relatively small group of viviparous (only representatives of Gyro- dactylidae) and another group of egg -laying types to which the overwhelm- ing majority of species are related. This division points, also, at the same time, to a considerable difference in the method of infection of the host be- cause the viviparous forms infect by means of direct contact with a host 109 when they are adult worms, whereas the egg -laying forms infect, in the free -swimming larval phase, through the medium which surrounds the host. In their turn, as was described before, egg -laying forms fall into two groups -- egg -laying proper, that is depositing eggs into the body of water in which the host and parasite are located, and into the egg-attaching group in which the eggs delay themselves for development on the body of the host. Evalu- ating what has been said above we can say that the deposition of eggs on the bottom appears to be more primitive, whereas the viviparous type with in- fection of the fish by means of contact appears to be more complex and un- doubtedly is the latest historical development. The sinnplest life cycle is of the form with a prolonged period of egg deposition in which eggs are deposited on the bottom of the water reser- voir and with a free -swimming larva which has the ability of infecting the p. 107 host in all, or more precisely, in almost all phases of its (the host's nobis) life cycle. Such a type of life-cycle we observe among fresh-water repre- sentatives of the genus Dactylogyrus. The most studied is the cycle of an important parasite, D. vastator Nybelin. Because of the fact that a disser- tation and a number of special works of N. A. Izumova (1953, 1956a, 1956b) are dedicated to the biology of this species, we shall dwell on the oviparous cycle only briefly. The worms deposit eggs which develop in different periods de- pending upon the temperatures of the water. A number of authors (Nybelin, 1925; Nordquist, 1925; Wunder, 1929, and others) maintain that D. vastator has two types of eggs --"summer", relatively small and developing quickly and "winter", large and developing slowly. According to Nybelin, during the warm months reproduction takes place only by means of "summer" eggs and during this period a number of generations of the worms take place. Then, with the arrival of low temperatures, the worms begin to deposit large "winter" eggs which hibernate at the bottom of the body of water and termi- nate their development toward the following summer. The worms them- selves all perish in the fall and are absent during the winter. Beth questions, i.e., concerning "winter" and "summer" eggs and about the existence of adults during the winter tinne, appear to be fairly complicated and were solved only in recent times, and mainly by the work of the Soviet researchers. During the study of the periods of the development of the eggs of ^ vastator , we established (Bychowsky, 1933d)that at a temperature of 21.5 to 24. 5° the larvae will emerge from the egg on the fourth day, at a temperature of 18. 2° on the fifth day, temperature 17. 7°--in six days, temperature l6.4°--the seventh day, and somewhat later we observed that at a temperature of 15. 5° the development continues for more than ten days. According to E. M. Lyman (1951a) who especially studied this question, at mean temperatures of 28° the development continues three days and at temperatures of 24 -- four days, of 20° --five days, 16°- -six to seven days, 12°- -ten to eleven days, 8°--27 to 28 days, 4°--is totally absent. In such a fashion, a severe lowering of temperature not only retards development but also 110 interrupts it for a more or less prolonged period. As regards morpho- logical differences between the "winter" and "summer" eggs one should consider them as nonexistent, or more precisely that the observed facts were not correctly interpreted. According to our observations and also according to the data of Kulwiec (Kulwiec, 1929), the same specim.en of D. vastator deposits, at any time, eggs which vary extremely in size so that some could be considered as "summer" and some as "winter. " How- ever, their further development is completely uniform and no difference is observed in periods of development. It is clear from these reproduced data that in the spring infection can take place from hibernating eggs, but there is no basis for acceptance of the hypothesis of "winter" eggs to explain this. The existence of adult individuals in the winter periods, which is denied by a number of authors, is actually indisputable. Thus, as early as 1929 during our student work on the trematodes of the fishes of the Volga River in the vicinity of Kostroma, we succeeded in showing that all the species of Dactylogyrus occur in the coldest months of winter on the most diversified fishes. An unusually low quantity of parasites and also a severe lowering of the percentage of infection of separate fishes constitutes a peculiarity of winter infection. All subsequent studies substantiated the given conditions. Thus, A. P, Markevich found Dactylogyrus and even their eggs in January and February on the gills of Carp in the Nikolsk fish farm (Markevich, 1934). In the work of E. M. Lyman (1951b) are reproduced data concerning the infection of Carp during the winter by gill trematodes D. vastator and D. anchoratus (Dujardin) in which it is clear that for D. anchoratus the percentage of infection remains very high during the entire p. 108 winter, whereas for D. vastator both the percentage of infection and the quantity of the parasites are lowered. From the work of Lyman it is also apparent that he also observed egg-laying by D. vastator during the winter. This appears to us erroneous. It is more probable that Lyman dealt with individuals which began depositing eggs after the transfer of infected fishes into the laboratory, that is during the changed temperature regime. Under natural conditions, the life span of D^ vastator, as has been pointed out in Chapter 2, fluctuates very much, but in summertime it is not less than 20 to 25 days in spite of the opinion of Groben (Groben, 1940)^ who believes that D. vastator lives only 10 to 12 days (including the embryonic development). The individuals infecting fish in the late autumnal period partly perish during the lowering of temperature and partly hibernate. In such a fashion the life span of the latter can reach 6 7 months. The life of the separate individual from the moment of emergence of the larva from the egg consists of several hours of existence in the free -swimming stage and then a period extending from the moment of the settling of the larva on the gills of the host lantil maturity, a period which among D. vastator under conditions of the Leningrad region, i.e., at summer water temperatures about 14 to 17°, continues for 6 to 8 days, and the interval of time from the beginning of maturity until death, which extends not less than 12 days. The deposition of eggs takes place during the entire life of the worms but 111 not with the same intensity (Fig. 119) depending upon external conditions, mainly on the tennperature and oxygen regime. Data of N. A. Izumova (see page 86 ) show that under average conditions in the Leningrad region during the summer, _D. vastator deposits from 4 to 10 eggs in the space of 24 hours. She also noted that under unfavorable conditions during the rising temperature and a worsening of oxygen regime the number of eggs deposited increases considerably. The observations of Izumova were conducted on worms which were located in natural con- ditions on the gills of their host. ■^ Contrary to her data, all infor- mation about the deposition of eggs of D. vastator cited in the works of Groben, Lyman and others has no significance to the understanding of the life cycles because it concerns the deposition of the eggs by worms which are located in artificial and obviously completely unfavorable conditions. These data basically can be utilized only for the clarifi- cation of the rate of the production of the eggs. An important factor to the p. 109 understanding of the nature of the life cycle of D. vastator is that in natural conditions the levels of in- fection in the host fluctuates, not only with the season of the year, but also with the age of the Carp. Thus, according to the data of Lyman (1951b) infection of the fishes takes place first at the age of not less than 10 days and mainly toward the end of the first month of their existence. These data are substantiated in the experimental studies of Izumova. During the following two months of the life cycle of the Carp, the percentage of infection and the number of the individuals of the parasite increase very greatly and later toward the fall-winter period, it (D. vastator , nobis) is encountered also among the older ages of the fishes on a considerably smaller number of individuals and in a decreased percentage of infection. The reasons for these seasonal age changes in the nature of infection have not been clarified and can be interpreted differently. Thus, one can suppose that a relative age immunity enters into play here, which, however, seems 8 9 10 II 12 13 14 15 16 17 18 19 Growth of worm in a 27 hour period Fig. 119. Dactylogyrus vastator Nybelin, dependence of the tempo of the deposition of eggs on the age of the worms. Observation on egg deposition of worms located in natural conditions on the gills of very young carp. Fish Industry "Ropscha, " Leningrad region (According to Izumova, 1953). 1--Very young fish. 2--Young fish no. 2. 3--Young fish no. 3. 4--Young fish no. 4. 5--Young fish no. 5. 112 improbable to us. In our opinion, the reasons for this phenomenon lie in the range of conditions for existence among various adult categories of the host, and in the lesser possibilities of the contact of the latter with free- swimming larvae, D. vastator (see also further page 110 ). It is possible, however, that different factors take place and also that the tissues of the gills of the carp of different ages possess unequal tenderness, and by this very fact the possibilities of attachment of the larva to the gills in different ages of the carp are not the same. Thus, the life cycle of D. vastator consists of three stages closely connected with the cycle of the host and with the yearly changes of the conditions of the body of water. Reproduction of D. vastator starts in the early spring and continues for the entire summer during which a signifi- cant number of generations are passed, and during the period of the warmest months the nunaber of parasites increases extremely. As a result of the fact that toward the period of mass emergence of the free-swinnming larvae the developing fish of the year are susceptible to infections and are located in places where a significant deposition of the eggs of D. vastator occurred, the bulk of the latter at first develops on young -of -the -year fishes and not on the older ones which go away into places which are not suitable for infection. Toward the fall the tempo of reproduction and the speed of embryologic development decrease and finally the period of winter depression begins during which the small number of worms which were preserved on the fishes decreases to such an extent that toward the spring only isolated individuals remain. In the spring the period of reproduction of the surviving individuals (including those •which spend the winter without reaching maturity in the fall) begins, and the infection of fishes takes place first by the larvae which emerge from the hibernated eggs, and then from the eggs deposited by the surviving adults. In the begiiuiing, the infection develops among the older ages of fishes and only later in the newly appearing generation. Thus, in natural conditions the crowding of fish is less and the conditions for contact between the larvae of D. vastator with different ages of the host are not the same and basically insufficient so that the infection of the fishes is usually small and the outbreaks of fatal epidemics are practically absent. The result is different in culture farms where artificial conditions inevitably lead to the increase of infection of earlier ages which causes epizootics of Dactylogy r us . Hence, the necessity for constant active reference of parasitologists to the conscious (detectable, nobis ) change in the character of the quantity and in- fection of D. vastator in order to prevent the outbreak of epidemics. The cycles of the majority of freshwater Dactylogyrus have a p. 110 similar nature and differ mainly in details. Thus, D. solidus Akmerow is apparently a more cold-loving type (Bauer and Nikolskaya, 1954), and in this connection in the conditions of our carp farms the nature of the change of the infection of fishes by it is somewhat different and the maximum quantities of the parasite fall at a time of the sximmer period. 113 Among Dactylogyrus the life cycle of _D. iwanowi Bychowsky, which parasitizes the Far-Eastern Rudd--Leuciscus brandti (Dyb. ), stands apart. Ugay,or Rudd as it is more often called in the Far East, is the only marine representative of carp in our fauna. It is a typical anadromous species.During its entire life it is encountered in the sea, sometimes far away from the mouths of the rivers and entering into the latter only for spawning: "In the Suyfun and other rivers entering into Peter the Great Bay it ascends (the rivers, nobis) when the ice begins to melt and sheds roe in the beginning of May-Jvme and during the sunamer up to September, and the individuals which finish spawning during the summer then descend into the sea; the immature ones are encountered all year round at the mouths of the estuaries; the young ones, having hibernated inthe river and having reached 7 to 9 centimeters in length, descend into the sea" (Berg, 1949). Although very insignificant and based predominantly on fixed material, our data show that infection by D^ iwanowi takes place in the river period of the life of the Rudd and that mainly the young individuals which are descending into the sea are infected. The worms live on their hosts more than a year, reach maturity during the marine period of their lives, and during the approach of the host to the river begin an increased deposition of eggs. What remains to be explained is whether a deposition of eggs takes place during the marine period of life of D^ iwanowi and what Is the fate of these eggs. Apparently, even if this deposition takes place, the larvae emerging from the eggs practically do not infect Rudd, because conditions exclude the possibility of the encounter of the larva with its host. Likewise, the secondary infection of the adult individuals which takes place in the fresh water is a more rare occurrence than the infection of the young, for the same reasons as were indicated for D^ vastator. Thus, the life cycle of D^ iwanowi (Fig. 120) (Fig. 120) already has a much more complex character and is adapted to the peculiarities of the biology of the host. We observed a singular life cycle in the parasite of the Zheltoperaya flounder (Green-flnned Flounder, nobis) , Llmanda aspera (Pallas)- -Protancyrocephalus strelkowl Bychowsky (Fig. 131). This species is encountered almost exclusively on mature flounders at ages ranging from less than a year to three years mainly along the coast or the zone close to the coast of the sea and at depths of up to 2 meters. For the understanding of the life cycles of Pr. strelkowi it is necessary to explain briefly the data concerning the biology of Its host, the Zheltoperaya flounder. The Zheltoperaya flounder is widely distributed in the Far East and is encountered at different times of the year at different depths starting from the littoreal zone to 180-200 meters and even deeper. The mature individuals, i. e. , the age cate- gories from four years and above, maintain themselves in the winter at great depths and migrate into shallow waters with the arrival of spring where at depths of from 8 to 20 meters they begin to spawn. Spawning usually takes place in June -July, after which the adult individuals spend a certain time in the same region feeding vigorously 114 and then towards October -November begin migrating toward the depths. The younger age groips also perform analogous migrations, but begin them earlier and proceed toward the shore at shallower depths and in the fall depart not so far as mature individuals. Thus, the majority of young flounders hibernate in depths of 15 to ZO meters. The roe of the Zhelto- peraya flounder is pelagic and the larvae which emerge from it direct them- selves toward the shore, and undergo a metamorphosis in the zone very close to the shore and remain until late fall. The migrations of flounders are closely linked with the temperature regime of the sea (Moiseev, 1946), 111 Fig. 120. Dactylogyrus iwanowi Bychowsky, schematic representation of the life cycle, somewhat simplified (the period of hibernation of the young Leuciscus brandti in the river is not indicated; and for the sake of con- venience it is understood that the young ones descend into the sea com- pletely). Explanation in text. According to our observations the infection of the flounder takes place only in the littoral zone and the reproduction of Pr. strelkowi takes place not during the entire warm period but mainly at the end of July and in August. This reproduction has a mass character. From our diaries it is apparent that in the Bay of Anama at the Island of Shikotan the accretion of the quantity of larvae of Pr. strelkowi on flounders of 13-17.5 centimeters 115 in length (that is, approximately, 2- or 3-year olds ) takes place at a fast tempo. The development of eggs lasts from 8 to 11 days and the further development of the larvae on the flounder continues very quickly, apparently with the same speed as among the Dactylogyrus. Taking into consideration that we found several hundred larvae that were in similar stages of develop- ment on the gills of the flounder at the same time and also taking into consider- p. 112; ation the small number of adult worms, one can consider that the deposition of eggs takes place in large quantities during a relatively short period. The infection of large individuals also takes place but both the percentage of in- fection and the quantity of parasites among them are very low. Thus, in the Bay of Anama we found Pr. strelkowi i n flounders of 28 to 32 centimeters in length (4 years and older) only 3 times among the large numbers of fishes examined and, in all cases, bearing a single individual each. From what has been said we can establish that the life cycle of this worm is adapted to the conditions of the littoral zone where Pr. strelkowi i s constantly pre- sent on its host. Infection of mature individuals is almost lacking pre- cisely because of the fact that adult flounders either connpletely or almost completely avoid these depths. We could not explain the continuity of the life of the worms with precision but it is evidently not less than 8 months, I because the three-year-old flounders depart into depths when they are highly infected and toward spring they return either completely uninfected or infected only rarely. Thus the infection takes place only among the ' young groups of fishes which do not migrate very far and which return to the shore earlier. Consequently, in the example of Pr. strelkowi w e see a special type of the adaptation of the life cycle to a determined age compo- sition of the host and to a determined place of habitation within the limits of the range of the latter. In the case of _D. vastator Nybelin, we could not precisely indicate the reasons for the weak infections of the older ages (of the host, nobis) and express only the hypothesis that here the absence ! of contact between the free -swimming larvae and the host and not an age immunity is of prinaary significance. But, in the case of Pr. strelkowi , we can ascertain that the absence of infections in older ages (of the host, nobis) is a result not of immunity, but of special correlations of the life cycles of the parasite and the host. I The life cycle of Diplozoon paradoxum Nordmann, a widely distributed and well-known parasite of freshwater carp fishes appears to be rather complicated. The basic stages in the life cycle of Diplozoon were described by early researchers, mainly by Zeller (Zeller, 1872c). Certain observations which coincide in principle with Zeller' s were also conducted by us. In the winter period the adult D^ paradoxum are located on the fish in an inactive state. According to Zeller, their sex system not only does not function but also their sex products are as yet developed very weakly. Thus, Zeller observed that a quick development of egg cells and vitelline cells takes place in the spring with the natural rise of the temperature of the water, or during the artificial transfer of the parasite with its host into a warm aquarium even in the winter, and that egg forma- 116 Littoral zone Open sea p. 113 c o ■fH +-> -tJ (D O to d ^^ ^ a, rt u ■^ J2 u to a CO C o Pi o X o u ft d I — I w u >< u 117 tion has begun on the fifth or sixth day. Our observations on the sex system of D. paradoxum give a picture similar to the one described for Polystoma integerrimum Froelich (see page 82 ). The wornnis examined during the winter have a fully developed sex system, and in the spring period it begins to act very quickly without any special period of acceler- ated development of sex cells. The change to the active state takes place much slower than in P. integerrimum , which is understandable when one takes into consideration the gradualness in the increase of temperatures in bodies of water where parasites and their hosts are located. The repro- duction of D. paradoxum which begins in the spring continues almost the entire sunnmer but the intensity of the deposition of eggs in May-June is significantly higher than in the following months. The eggs of D. paradoxum basically remain on the gills of the host, and Zeller observed up to 100 in each fish with 3 mature parasites under artificial conditions. The larvae emerge from the deposited eggs on the 12th to the 17th day according to p. 114 Zeller (according to our data, 9-lOth day) and after a short time they in- fect fish. The diporpa larvae which settle on the gills live for a certain length of time singly and their growth develops rather slowly. After reaching a determined stage of the development of the attaching apparatus (2-3 pairs of clamps), a large part of the larvae ceases further growth if it doesn't meet the same larvae with which it unites in pairs, grows to- gether and continues mutual development. The larvae which remain single live for a sufficiently long time, but all perish toward the winter. The individuals which united in pairs begin to grow much more quickly than the single ones and toward the spring of the following year they reach maturity. As is apparent from what has been said before, the critical moment in the life of D. paradoxum is the union of a pair of individuals, without which further development is impossible. Taking into consideration that the periods of the emergence of the larvae from the eggs are greatly extended one would expect a large percentage of loss of some of the worms; however, this is net observed in nature. The reasons for this appear to be a repeatedly noticed union of the larvae of more or less different ages. Thus, relatively slow growth of the larvae is an adaptive peculiarity to the singular life cycle of ^ paradoxum . All in all, the life cycle of the latter (Fig. 122) has a number of primitive traits characteristic of the forms with extended egg deposition, and just as many highly specialized traits which are determined by the peculiarities of the sex cycle. In addition to what has been said before, one must note still another peculiarity in the nature of infection of the host: Younger hosts are infectod less than older. Thus, those of less than a year are completely free of D. paradoxum, the yearlings either are completely vm- infocted or infected exceptionally rarely and weakly and are often infected not by pairs but by a single diporpa. How this phenomenon can be explained one cannot say exactly; however, we are certain that here take place the same circumstances about which we have often spoken earlier, that is, different placts of location of older and younger fish. In connection with this is the fact that the eggs of D^ paradoxum are found on the gills the fishes of younger ages, which as a rule keep themselves separate from the older ones. 118 p. 115 J^ ■i-i '*-! O ^ 0) 4-J c t X CD •7-* • -- -4— > 0) c ■4-> c (U rt ^1 B C »-i (U X u m Id o O -a X o ni u nJ A. O O N O I— I P. • r-t P 0) .—I "^ o .y C -a ^ M O D- a o I— I t3 • o I— 1 jh MH U •■-I nJ 119 have very little probability of being infected with the larvae of D. paradoxum. Certain observations of the life cycle of Mazocraes alosae Hermann were conducted by us on the Caspian Sea during 1931-32. The hosts of this parasite in the Caspian Sea are numerous types of herrings among which we dealt basically with Alosa brashnikovi (Borodin), A. saposhnikovi (Grimm), and A. caspia (Eichwald) in the region of the Island of Sara. The study of the worms during May and June disclosed a strong cyclical nature in the period of reproduction of this species and conse- quently a quite complex character of the life cycle. According to our observations the herring bears only large mature M. alosae on their gills until the naiddle of May, and the latter do not form or deposit eggs. In our diaries there are notes that even in artificial conditions we were unable to obtain deposition of eggs from the worms. The beginning of the formation and deposition of eggs was first noticed in the beginning of the second half of May, and this process took place in a very turbulent fashion. The eggs are deposited by worms on the gills and attach to them very tightly by the tens and even hundreds on a single fish. From experimental data, we know that the deposition of eggs of M. alosae takes place during 4 to 6 days. Taking into consideration that in nature temperature con- ditions are different, we can consider the periods of development of eggs in nature equal to 8 to 10 days. This fully corresponds with our obser- vations. Thus, the first depositing individuals of M_. alosae were noticed p. ii6 May 19th and already 8 days later we discovered larvae on the Kislerov Herring which liad just settled. ^ The number of the larvae which settled on _ In 1955 on the Isle of Sara we observed egg depositing individuals of M. alosae even earlier- -May 13. the gills of the fishes is not very great. According to our notes, it fluctu- ates from five to fifty- -mostly around 20, 1. e. , it corresponds to the number of adult worms normally observed in nature m other periods of the year. The period of infection of herrings apparently is not very long-- within limits of a month or less. The further growth of the settled larvae takes place fairly rapidly; thus already a fortnight later (13 June) we found young M. alosae with three pairs of clannps and with the fourth in the process of inception. Thus, the complete formation of the attaching apparatus takes place during 15 to 20 days, on the average. In view of what has been said before and also from the obser- vations on the nature of infection of herrings of the genus Alosa from the Caspian and Black Seas, one can visualize the life cycle of M^ alosae more or less exactly (Fig. 123). As is known, our southern herrings approach the shores or enter the rivers for spawning for relatively short periods, mainly in April-June. After that they descend from the rivers into the sea, or depart from the shores and maintain themselves in the 120 depths: according to the data of Svetovidov (1952), in a scattered fashion and, in addition to that, the younger ages keep themselves separate from the old ones. Thus, the basic favorable time for cross -infection of the host is the period of the approach of the herring toward the shores for spawning. The mass deposition of eggs of M. alosae coincides precisely with this period. Undoubtedly the probability of infection of the host would have been exceedingly small if the eggs were deposited directly into the water, for during the migration of the herring their scattering would have been exceedingly great. Thus, it is clear what a great adaptative significance the deposition of these eggs on the gills of the host by M. alosae has. From this, certain peculiarities of the infection of the host of different ages emerge. M. alosae is encountered only on adult fishes starting with three-year-olds (let us remember that as a rule the majority of Caspian herring spawn at this age for the first time and that two-year -olds spawn only in rare cases), that is younger ones are not infected with M. alosae, which is easy to understand because the contact betv/een the younger and older ages of the herring is very insignificant, if it isn't practically absent all together. It isn't clear whether the less than one-year-old or the yearling herring are in a position to be infected. In nature they never meet with larval M, alosae capable of infecting them, whereas the two-year-olds have more chances to enter into contact with the older ages there and con- sequently have a greater possibility of being infected. Actually in rare cases we observe this in nature. The question about infection of fishes in fresh water appears unclear in the life cycle of M. alosae. We have no factual observations on this but it seems to us that, taking the biology of the host into account, this possibility is not excluded. Further research will verify the correctness of the supposition. Apparently the life cycles of two species of Octostoma which para- sitize the Japanese mackerel- - Pneumatophorus japonicus (Houttuyn) are close to the life cycle of M. alosae. In nature we see that Oct. scombri (Kuhn) and Oct . minor (Goto) (Fig. 124) are encountered only on adult fishes, beginning with two-year-olds. At the same time, the parasites which are encountered are always of one size --fully matured. Hence, p. 117 one can suppose that the multiplication and deposition of eggs of both species have a periodic nature. The Japanese mackerel usually maintains a depth of 20 to 40 meters in the open sea and connes to the shores in large schools for spawning in May and June. The spawning extends approximately from the middle of June to the middle of July within 5 to 6 miles of the shore. The young ones which emerge from the roe wander toward the shore where they remain the entire summer, going to the depths in the late fall and returning (to the shore, nobis) early (the next spring, nobis). In such a fashion, contact between the early ages and the mature mackerel is absent. Because of that and also of the fact that, as among M. alosae, the eggs of both types of Octostoma are detained on the gills of the host, one can expect that the 121 ^SmBSKUl-'iM c •r-1 +-» nJ -M c 0) CO 0) ^1 ex (U Vl , 4-1 o X • f-l o> rt -M g *r-t 0) o o (0 ■4-1 ni C frt c I— t (i (X 0) ffi . (U (1) 1—1 frt o ffi >< o u n] (U (0 f— 1 o N ci S ro fvj .— t • 00 •l-l h 122 peculiarities of the infection of the naackerel correspond to those of the herring parasite, and the life cycles of all three species are actually very close. We cannot fail to notice, also, the systematic proximity of both genera of monogenetic trematodes. Fig. 124. Qctostoma sp. sp. from the gills of Pneumatophc rus japonicus (Houtt. ) from the region Yablochnoii (southern Sakhalin, Se i of JaoanX A- -Armature of the copulatory organ of O. minor (Goto); I. --Middle hooks of the attaching disc of O. minor (Goto); G--Armatur2 of th^ copulatory organ of O. scombri Kuhn; D- -Middle hooks of the attachii g disc of O. scombri Kuhn. Interesting observations on the life cycles oi Microcot\ le gotoi Yamaguti were successfully conducted during works on Southern Sakhalin in 1946 and continued in 1949 on the Island of Shikotan. M. gctoi parasitized natural marine fishes of the genus Hexag rammos , mainly nn _H. oct ogrammus (Pallas) in Southern Sakhalin and on H. lagocephalus (Pallas) near t ae Island of Shikotan. In our opinion, the data on the biology of these fishes i re still insufficient, and because of that we should first show the materials vhich we have on the life cycle of M. gotoi a nd attempt to compare them w th infor- mation availa.ble about the Terpug (rock, trout, starling, nobis). p. 118 123 In summertime up to the middle of August only mature para- sites are encountered on both types of fishes and (then, nobis) only on older fishes. Thus, M. gotoi is encountered on H. octogrammus starting fronn two-year-olds (the lenirths of the fishes are from 18 centimeters) and on H. lagocephalus - -among fishes with sizes from 20 centimeters (apparently also two-year-olds). Mainly toward the middle of August we observe Microcotyle on both fishes with a large number of eggs in the uterus which are deposited simultaneously by the worms and then a new portion of eggs begins to accumulate in the uterus which was just emptied. An especially intensive formation and deposition of eggs of M. gotoi takes place during this period. This process continues until the second half of September when apparently it ceases or in any case slows down considerably. Emergence p. 119 of larvae and the infection of fishes from the eggs deposited in the water begins at the beginning of the third ten days in August in Southern Sakhalin and in the first ten days of Septennber in Shikotan. Inasmuch as the larva which has just emerged from the egg does not yet have clamps and since the latter are incepted gradually in proportion to the growth of the larva we can, on the basis of the structure of the attaching armature of the larvae, judge about the periods of infection of the host, the intensity of infection and also about the length of time during which it takes place. In the beginning, the intensity of new infections builds quickly and then gradually decreases until young stages are almost completely absent. According to the time, it is apparent that in outhern Sakhalin this process is most intensive at the end of August- -the beginning of September, and on Shikotan- -some- what later. A strong decrease in infection takes place apparently in both regions in October (on Shikotan we did not observe the end of this process). Thus the emergence of larvae from the egg takes place very intensively only from 15 to 20 days, although it extends generally up to a period of almost one and one -half months. The infection of fishes takes place unequally according to ages. The most strongly infected are yearlings, which until that time were conn- pletely free of Microcotyle. Along with them the older stages are also in- fected, although in much smaller numbers and percentages and by a smaller number of parasites. In this case, a great role is played by the location of the fishes of different ages. Thus, fishes up to 20 centimeters in length, i.e., until the age of two, keep much closer to the shore all the time, whereas the older ones are encountered in shallow places in much smaller numbers and apparently rarely after spawning. After the infection of the fish, the worms grow rather slowly so that at the most after ten days they have 10 to 15 clamps instead of the 38 to 42 pairs characteristic of adults. Apparently the full development of the attaching apparatus is delayed until the late fall and the worms reach nnaturity towards the spring -fall of the following year. The data obtained fully correspond to the sketchy infor- mation about the biology of the Terpug (Rock, Trout, or Starling, nobis). It is known that the latter does not reach maturity before the age of two years. The adults usually maintain themselves at depths of more than 10 124 p. 120 <0 X 4-> VH o fl o • rH -M Oi -M fi (U CO i) u n) 3 .—I ao CX X nJ g W nJ t>H 1) o >< o u W) a> OJ ^ o u o y in fM 00 125 to 15 iTieters and approach the shore only in spring. Spawning apparently takes place in August and during that time the adult individuals approach 1 It is known precisely that near Hokkaido H. octogrammus spawns in the second half of August; near Shikotan the individuals of H. lagocephalus which had just spawned were encountered from the end of August. the shore very closely. After spawning, adults return to the greater depths. The young fishes in ages up to two years basically nnaintain themselves in shallow water the entire sumnner, almost right by the shore, and in late fall migrate to greater depths. Juxtaposing the data on biology of fishes with the parasitological data, we see that the life cycle of M. gotoi (Fig. 125) is fully adapted to the peculiarities of the life cycle of the fishes. Also the reasons for the absence of larval stages and developing worms on the adult fishes until fall and also the absence of infection of young ages become clear. At the same time, the data cited indicate that the life span of M. gotoi individuals is not less than a year and most likely is even longer, be- cause on adult two-year-olds we find worms of somewhat lesser size than on the older fishes. The life cycle of Polystoma integerrimum Froelich is extremely complex. Excellent observations of P. integerrimum Froelich, which para- sitizes different frogs, mainly Rana temporaria Li.,were expressed in the works of Zeller (Zeller, 1872a, 1876) and Gallien (Gallien, 1935). We also have considerable material. It was obtained as result of three -year obser- p. 121 vations in 1927 to 1929 in the region of the Peterhof Institute of Natural History. Because of the differences of geographical points of research be- tween our material and the information of the above-mentioned authors, there are a number of differences; mainly in the lengths of different processes. Because of this, we shall outline the life cycle of ^. integerrimum in general traits and then reproduce certain calendar (chronological, nobis) data based on our and Gallien's observations. The examination of the life cycle (Fig. 126) begins best with the winter period of the year and with fully adult indi- viduals --4 to 5 years. At this time all the wornns have a fully developed sex system completely ready to begin functioning but still inactive. The worms are located in the urinary bladders of the hibernating frogs. In early spring as the latter emerge from that portion of the body of water in which hiber- nation took place, the sex system of P. integerrimam begins to function and a few days later, during which the "excision" of egg cells (see page84 ) takes place, egg deposition begins. Toward that time the frogs pair and again depart into the water to a place where a day or two later they deposit roe. The eggs of P. integerrinnunn are deposited in the same place and almost at the same time as the roe of the frogs. However, the deposition of the roe terminates somewhat earlier than the deposition of the eggs of P. integerrimum because the former usually takes place within 6 to 15 days 126 and the latter from 10 to 20 days, and sometimes it is delayed for a certain additional period. The development of eggs of P. integerrimum in natural conditions is rather lengthy. Depending upon temperature conditions, it lasts from 20 to 30 days in the Leningrad region and from 40 to 50 days in France (according to Gallien). The free -swimming larvae emerging from the eggs seek their hosts, which happen to be tadpoles which at that time are undergoing different stages of development, starting with the appearance of inner gills. The fate of the larvae becomes different after their attach- ment on the gills of the tadpoles. If the larva attaches itself to the gills of a very young tadpole it begins to feed intensively and grow fast, changing into a special mature form, the so-called "gill" P. integerriinum. In the case when the larva falls on more mature tadpoles they feed less intensively and grow more slowly without the development of the sex system (their fate will be described somewhat later). The "gill" P. integerrimum reach full maturity 20 to 25 days after the settling of the larvae on the gills of the tadpole and from that time begin to produce eggs. The gill form is very interesting in structure because it differs significantly from P. integerrimum from the urinary bladder. The gill P. integerrimum (Fig. 127) has a less distinct, so to speak, broadened configuration of the body and the attaching disc is not delineated from the body, the interior organization is also sharply distinct. The intestinal tract has a small number of lateral growths and interior anastomoses and the location of both is less regular than among P. integerrimum from the urinary bladder. There are especially significant differences in the structure of the sex system. The ovary of the gill form is very long and almost straight with a flask-like widening at the anterior end filled with rapidly developing obgonial cells. Oocytes in the ovary lie one after another in its longer part and are efferred (expelled, nobis) from the ovary according to their degree of maturity. Generally the shape of the ovary of the "giU" P. integerrimum resembles thc-t of the young, still immature P. integerrimum of the urinary bladder (Fig. 128). Among the gill forms the vaginal ducts are completely absent and actually, so to speak, there is no uterus as among many of the lowest monogenetic trematodes, but only an ootype in which a single egg is formed at a time P- 124 which is immediately carried outside. According to the data of Gallien^ the ductus genito-intestinalis is absent among the gill type of the parasite, and apparently it is really so. The male sex system is represented by a round testis and a seminal duct which opens into the copulatory organ of identical structure to the one of P. integerrimum from the urinary bladaer. According to Gallien, the seminal duct is absent and the copulatory organ is not connected in any way with the testis, so that it represents, in such a fashion, only a rudimentary remnant. According to Gallien, fertilization takes place through a special duct uniting the male and female sex systems. In his time Zeller also wrote about this duct. Our observations do not substantiate these data. Fertilization of gill forms takes place just as among lowest monogenetic trematodes --not through a special canal, but through the ootype. The life span of the gill form coincides with the period of existence of the inner gills of the tadpole --with their disap- pearance, the "gill" P. integer rinnum perishes. The deposition of eggs 127 128 p. 123 ti o ji • H ■*•> ■!-> u ■!-> G o V-l ■t-> u o u ^ • rH • r. ■4-> nl 0) B o • r-l in X ^ (U X v-i • u o (L) .f-< O f— t u c 0) nJ a) 0) -M CO B CO (U O U .r-i a< (i ;h o (U V ■1-1 >- bO 0) .r-4 fl a O s o • 4-> (U 03 1— 1 f—t o >< o o Oi a; •r-l sO l-H (NJ (U 1— 1 ■w •r-l V+-I o Cn 129 among this form, which starts with the appearance of the approach of maturity, continues until the very death of the wornns. The free -swinaming larvae emerge from these eggs after approximately 15to 20 days because at that time the temperature conditions in the body of water are more favor- able. The larvae of the gill forms, just as the larvae of P. integerrimum from the urinary bladder, attach to the gills of the tadpoles. Their further fate is the same as that of the larvae of P. integerrimum of the urinary bladder which settled on the gills of older tadpoles . Morphological differences between both are absent, Fig. 127. Polystoma integerrimum Froelich, mature gill form from the gills of tadpoles of Rana temporaria L. from Peterhof (Leningrad region). Natural size 1. 2 mm. Fig. 128. Polystoma integerrimum , Froelich, young immature worm from the urinary bladder of year and one -half old Rajia temporaria L. from Peterhof (Leningrad region). Natural size 1. 5 mm. p. 125 and during the metamorphosis of the tadpoles they pass from the gills through the entire intestinal canal into the urinary bladder. In the urinary bladder and sometimes somewhat earlier, the larvae begin gradually to acquire the final structure of the attaching disc, which toward winter be- comes fully formed with all three pairs of suckers and with a middle pair of chitinous hooks. Further growth of Polystoma takes place during the following summer and finally they reach maturity in the third year. It must be indicated that the first maturity takes place with the presence of an ovary of different form than among four -year-old worms and with testes of smaller sizes. The deposition of young mature individuals of the urinary bladder takes place just as among older ones but begins somewhat later and the number of eggs deposited is smaller. 130 In the conditions of the Leningrad region during the period from 1927 to 1929, we observed the emergence of frogs from their places of hibernation in the beginning of the third ten-day period of April and the beginning of the deposition of roe by them (see Fig. 129) as early as the 25th to the 26th of April. The latter (deposition of roe, nobis) continues usually for a long time, often until the end of the first ten days of May and often the first tadpoles begin to appear by this time. Correspondingly, the first copulating P. integerrimum were observed from the 22nd of April, and the beginning of egg deposition from the 24th to the 25th. The deposition of eggs by worms continues until the 10th to the 15th of May. The first larvae usually appear on the gills of tadpoles from the 12th to the 15th of May and adult gill forms are discovered from the first days of June at the earliest and most often from the 10th to the 15th of June. The overgrowing of the gills and metamorphosis of the tadpoles and consequently the death of the "gill" P. integerrimum and the migration of the larvae into the urinary bladder of the young frogs begins about the middle of July and extends for 10 to 15 days, depending upon the peculiarities of the year. The departure of the young frogs for hibernation and the cessation of growth of young Polystoma until spring take place before the departure of the adult frogs from hibernation (October) and in the main coincides with the cold spells of the middle to the end of September. According to the data of Gallien, in France, (the region of the Department of Vosges near the village of Hansel) the deposition of eggs by P. integerrimum begins from the 25th of February and continues until the 25th of March with the maximum occurring about the 5th to the 15th of March (see Fig. 130). The emergence of the larvae and the infection of the tadpoles take place from the 15th of April to the 15th of May. The adult gill forms appear from May 10th, and their egg deposition lasts until June 15th. The eggs of "gill" P. integerrimum develop in 20 to 25 days, and the ones which were deposited after the first of June yield larvae which do not find tadpoles suitable for infection (metamorphosis has already begun) and for that reason are condemned to death. Correspondingly, according to the data of some authors, the roe of the frog is deposited in March mainly from the 15th to the 20th. The tadpoles emerge from the first days of April and (continue, nobis) approximately uitil its second half. The metamorphosis of the tadpoles begins from the 10th of June and basically ends before the 20th. The difference between our data and those of Gallien consist not only in the fact that all the processes observed by him take place earlier, which is absolutely natural, but also in the fact that in our opinion some of his statements are erroneous and demand verification. Thus, first of all according to Gallien, the deposition of eggs of P, integerrimum in the spring significantly precedes the deposition of roe by the frogs. As is apparent from the data published by him, this difference consists of a minimum of 15 days. Taking into consideration all ihe peculiarities of the 131 p. 126 q; bo P P W o p Q o ^C u CO 0) •p •H M-l (1) 4-> C H C 0) o c o o ji: •H u ■P 0) (0 4-> 4-) i H O Pu CT> CM c o •H lunuiujaSsjuT buiojsAxoj •H b4 132 p. 127 I CD K I ^ o \ W |s ^\ a eV o 4-1' D ° ™\\ m \ en bo \ O o o- 0) ^-^ \ U o t»in o ■s^ « "f H n 8^ 0) ^ — • c X X'- 03 u • fH <+H 0) .— ) j3 dJ -«-> (0 ^H a o (U (1 K -d o m o GO 1 lU f— t o CO f— 4 (J > CO a d (Ti (1) o ■t-> ni bO d CO a • a J3 ni ..H in CO 1— ( u d en «J o .r-( •* • w-t j3 d •* H 0) 1—1 1-1 d 1— ( f— 1 o (;) O o o V uinuiijjsSsjuT BuioasAjoj a o OD I— I o o en (30 P4 o (0 o , , O d 01 d 03 O u o (i () > XS 0) 0) J3 m 4-1 • rH 0) d 4-> Xi a +-> 00 >4-l o d •t-i ^4 D. O (ll (P o (U W u !>^ nt 133 region of his research, this seems improbable to us because the frogs never (rarely?, nobis) are found at the places of deposition of the eggs fifteen days before spawning, and this possibility takes place in certain p. 128 exceptional cases but not as a rule. Hence, his data concerning the development of the eggs in nature during 40 to 50 days also seem improbable to us. The same also can be said concerning the data of Zeller. The second basic difference between our and Gallien's material is that the gill forms produce eggs which, according to our data in the main produce larvae capable of infecting tadpoles, whereas according to Gallien a large part of them develop practically as "non-breeders" because the larvae which emerge have no chance whatsoever of infecting tadpoles. Thus, in the Leningrad region the gill forms develop during the first 20 to 25 days of June, whereas in France, according to Gallien, during only 10 days in the middle of May. In connection with these peculiarities of the develop- ment of tadpoles, the gill form.s lay eggs in our region in about 50 days, but in France in about 35 days. As a result, the larvae emerging fronn the eggs of "gill" P. integerrimum in the Leningrad region succeed in infecting tadpoles for 50 days and perish during the last 5 days at a maximum, where- as in France the emergence of the larvae takes place during 35 days and the infection of the tadpoles--the first 20 days and not 15, i. e. , 43 per cent of the time the larvae do not find hosts for themselves and perish. It seems to us that these data of Gallien demand re -examination- -we think that here are certain inaccuracies of observations. As is clearly seen from the attached diagrams (Figs. 129 and 130), all the rest agrees fairly well and shows striking lation of cycles of the host and the parasite in different geographical locations. Before passing to certain general considerations about the life cycles of egg laying of monogenetic trematodes we do not think it would be out of place to cite an example of a break in the link between the biology of tadpoles and P integerrimum which we observed in 1929. In one of the ponds of the Sacred (Forbidden, nobis ) Park of Peterhof of the Institute of Natural History, the deposition of frog roe and of ^ integerrimum took place near the south bank. Because of the land breeze, the main mass of tadpoles which had just emerged from the roe found themselves at a distance of 2 to 3 meters from the place of spawning. As a result though 100 per cent of the tadpoles which remained (in place, nobis ) were infected by P. integerrimum, 100 per cent of the tadpoles which were found to the side were uninfected. Thus, a circumstance which may at first glance appear insignificant, such as a distance of from 2 to 3 nneters, did not permiit the union of the links of the chain of the life cycle of the parasite. Summarizing our information about life cycles of egg -laying forms of monogenetic trematodes, we must note first of all their increased adaptability to the cycles of the host. Even in the simplest cases, a number of peculiarities are apparent which point to the very long period of the working out of the adaptations of the parasite to the peculiarities of the life cycle of the host, and this under the completely determined conditions 134 of the existence of the latter. The peculiarities of the cycle of Monogenoidea find a considerable reflection in various adaptations which arise at first in the sex cycle of the animals, and also in the annual cycle of development. First of all, without any doubt, common historical orientation in the develop- ment of peculiarities of action in the sex system proceeds along the line of the gradual transition from an extended period of egg-laying to its con- traction (shortening, nob is) to a greater and greater degree, which we ob- serve among the fresh water as well as among the migratory and purely marine forms. This is especially evident among the parasites of the Amphibia, i. e., hosts which change their means of habitat from the water to the land during their life span. The reasons for this historical process, p. 129 which takes place with various degrees of intensity among various groups, are undoubtedly caused by the necessity for creation of more favorable conditions for the infection of hosts. At first sight, the presence of an extended period of egg-laying appears to be more favorable under con- ditions of continuous (not apportioned, nobis) egg production; however, this is completely untrue. It is wrong because the basic factor is the necessity of infection of very mobile hosts by the free-swimming larvae of the parasite. In connection with this, the presence of contact between both, in time as well as space, is indispensable. The probability of such a contact under the conditions of extended periods of egg -laying is sharply lowered, inasmuch as among a considerable number, if not the great majority of the forms, the eggs do not remain on the fish. In such a fashion the necessity, which was pointed out by us, arises for an increase in the probability of contact in time and space between the two links of parasitic cohabitation during the presence of favorable conditions of the surrounding medium for the development of eggs and the infection of the host. As we see, this is attained by the decrease of the periods of egg- laying and the concentration of the latter in a more limited region. We note also that the attachment of eggs on the body of the host serves the same purpose--the concentration at the same time of a larger number of larvae within a specific territory. The concentration of the larvae which infects the host is acquired not only by the contraction of the period of egg -laying but also by the rationing of the latter. In separate cases, this apportioning of the egg-laying is carried out differently. Thus we saw that anaong a number of worms this is linked with the simul- taneous deposition of eggs joined by filaments, or little feet and filaments, to each other (a number of Microcotyle and others, see page 90), or with the speed of deposition at a determined time of the day or determined con- ditions of the external medium (many lowest forms --Dacty logy ridae and others). Finally, among P. integerrimum t he apportioning of the de- position of eggs is connected with the peculiarities of life activity of the host, because the eggs are ejected in large numbers periodically during the emptying of the urinary bladder of the frogs. 135 1 Indications to the effect that at the time of deposition, P^ integerrimum extends outside from the cloaca are not substantiated by our observations. The shortening of the period of formation and deposition of eggs creates a necessity of a large number of morphophysiological peculiarities in the functioning of the sex system. As we saw in the example of P. integerrimum from the urinary bladder, the yearly cycle of the sex system is completely subjugated to this problem and the processes of oogenesis and spermatogenesis, of the formation of vitelline food cells, the production of all auxiliary glands becomes strictly cyclical and takes place in such a fashion as to make possible the maximal use of all sex products which are available in the shortest period of the egg -laying. This is especially noticeable in comparing the characteristics of action of the sex system and the morphological peculiarities in both forms of P. integerrimum . We will note once more that "gill" P. integerrimum with an extended (although rela- tively short in time) period of the action of the sex system do not have a uterus but only an ootype, they have a different form of the ovary connected with a gradual ripening and expenditure of egg cells, and they have no vaginal ducts, etc. The differences in the deposition of eggs of both forms are closely related to the peculiarities of life and location of the stages of development of frogs infected by them. P. integerrimum from the urinary bladder has the opportunity of depositing eggs vmder conditions favorable to the subsequent development of the larvae only during the short period of the presence of the frogs in the body of the water at the time of their spawn- p. 130 ing because at another period the frogs are located in a different medium of habitat, and the eggs of the parasite deposited at the time are inevitably condemned to death. The gill form of P. integerrimum parasitizes tadpoles for its entire life and perisheswith their metamorphosis, consequently eggs deposited by it during the entire period of egg -laying fall into the medium favorable for the development and, as we saw before, have considerable chances for infecting the host. Along with the changes in the structure and functioning of the sex system, a number of adaptations toward peculiarities of life cycle is reflected in the structure of the eggs and also in the place of their location after deposition, as was previously mentioned. The re- tention of eggs on the body of the host is an important adaptation among many forms parasitizing fishes which lead a gregarious form of life and which perform considerable migrations. Among parasites of such fishes, it gives the same result as rationed egg -laying, as was already noted. However, here we encounter the substantial question of cross -infection of the fishes for without the latter the probability of the flourishing of the parasites as a species would have been extremely small. Increased in- fection of the same individual of host by newer and newer individuals would have worsened the conditions of existence of the host and by that very fact would have influenced negatively the condition of the existence of the parasite 136 itself. As was already indicated (see page 93), we clearly differentiate two periods in the life of the free-swinnming larva: non-invasional, when the larva is still not in condition to infect the host; and invasional (there is still another non-invasional period when the larva already is not in a condition to infect the host and thus is condemned to perish). The first of these enumerated periods is of special and extremely important signifi- cance because it enables the larvae emerging from the egg which is located on the host individual to infect another individual. In addition to the presence of morphological peculiarities, this is accomplished by the action of a positive phototaxis which has a direct significance in the dissemination of the larvae, whereas the relative speed of their mobility creates the possi- bility of a sufficient eloignment (separation, nobis) of the host on which the parent individual was located. The periods of development of the eggwhich undoubtedly also have adaptive significance are also closely connected not only with the internal peculiarities but also the external ones, and in the first order primarily with the temperature factor. This is clearly apparent in the case of "winter" eggs of Dactylogyrus vastator Nybelin and in the case of the coincidence of the periods of development of the eggs of P. integer rimum with the time of the development of roe and the larvae of the frogs which also depends on temperature. The historical process of the adaptation of the life cycle of the parasitic nnonogenetic trematodes to the peculiarities of life of their hosts proceeds along the line of limiting the possibilities of infecting unusual hosts or unsuitable stages of the life cycle of the host and leads in a number of cases to the development of a very narrow specificity in the true sense of the word. However, the life cycle of monogenetic trematodes reveals to us also a number of other methods of limiting in tinne and space the possibility of infecting hosts during less suitable stages of their existence, while preserving the potential capabilities toward infecting any stages and even other types of hosts. This extremely important pecixliarity is of tremendous biological significance. This question will be analyzed in detail in the chapter concerning specificity and incidence of occurrence of Monogenoidea (see pages 283-299 ). In the process of adapting to the infection of the host during the specific stages of its life we see two basic tendencies, the first of them leads to the development of adaptations toward infection and conditioning p. 131 the entire life cycle of the parasite to the younger ages cfthe host as takes place for instance among Protancyrocephalus strelkowi Bychowsky and the second leads to the ability of normal infection of the host, basically in its younger stages but after the parasite has reached maturity on adult indi- viduals. Apparently both tendencies are connected not only with the peculi- arities of the embryology of the host but also with the degree of advance- ment of organization of the parasites and the duration of their lives. As a rule the first tendency is observed among the lowest and the second among the highest of monogenetic trematodes. When we speak about yoxing stages 137 of the host we mean, in the majority of cases, individuals up to two years old among polyannual hosts or even younger annong quickly-maturing and growing fishes; however, one must bear in mind that for each type of host of egg -depositing Monogenoidea there is a proper period before which it (the host, nobis) is not infected. The reasons for this are not clear and it is possible that they are hidden in the nnorphological peculiarities of the gill apparatus which the large mass of monogenetic trematodes parasitize. N. A. Izumova, who was interested in this question, established that among Dactylogyrus vastator the infection of young carp is possible only when they reach the sizes from 10 to 12 millimeters and she came to the conclusion that this stands in direct relation to the degree of morphological differentia- tion of the gill apparatus of the fishes. The representatives of the viviparous family Gyrodactylidae have a special type of life cycle. Its basic peculiarity appears to be the absence of a special morphological differentiating stage which serves for the infection of the new individuals of the host. The infection, as we succeeded in establishing in special studies, takes place by fully mature parasites which transfer from one host individual to another when they come close to each other. One must say, however, that as yet much re- mains xinclear because the reasons causing the wornns to leave the host are | not fully understood, for we never observe direct contact between fishes in | normal conditions, even among the majority of gregarious forms. Con- I sequently, the worms and especially those which are located as a rule on ' the gills must make special effort to come out of them and actively try to transfer to another host. We hope that further experimental research will clarify this interesting question. The life cycle of Gyrodactylus has ap- parently a relatively simple character. Multiplication of worms takes place during the entire summer period and apparently more or less evenly all the time. The daughter individual is born when it is already fully formed and does not differ from the miother individual either in structure or in size (Fig. 131). Based on our observations of Gyrodactylus sp. sp. from the Stickleback, in the mother individual, after a rather short period of time following the birth, a new egg enters the uterus and begins to cleave and the process of its development until birth of the new daughter individual lasts normally about 4 to 5 days. The number of births in one mother indi- vidual has not been exactly ascertained, but according to the indirect evidence it is not less than 3 to 4. We happened to observe that after one of the births of the daughter individuals the mother individual almost immediately perishes, whereas in other instances the mother individual after a certain period of i depression becomes normal, beginning to feed and to move actively. Thus, | according to all observations the life span of a particular individual Gyro- dactylus lasts not less than 12 to 15 days and possibly even considerably longer. The fate of the daughter individual is somewhat different than the mother individual, for after the birth it has already in the uterus a strongly developed p. 132 embryo which is born approximately a day later and which in turn contains an embryo in the uterus. Since up to four ennbryos usually result from one 138 egg, as was indicated before, we obtain four unequal individuals following their birth. Thus, the first born individual has in its uterus three embryos lying one inside the other, the second- -two, the third- -one embryo, and the fourth- -none. In such a fashion the first three daughter individuals differ from the fourth by the fact that *" up to the beginning of the develop- ment of the embryo formed from its own egg they must give birth to one "remaining" embryo from the same egg cell as they themselves are. In m- contrast to them the fourth individual begins to give birth only to embryos resulting from its own eggs. This difference exists in each generation of Gyrodactylus and in such a fashion ^ each individual has differences with- in the first period of its existence. From the observation on the incidence of different types of Gyrodactylus it is possible to conclude that here also the cycles differ considerably. Thus, certain types are encountered only on young indi- viduals of the fishes and are always or al- most always completely absent in the older ones [for Instance, G. proximus Bychowsky and Poljansky from Pallasina barbata (Stelndachner)] and on the other hand, other types are discovered mainly on groups of older stages of the host [G^ marinus Bychowsky and Poljansky from Cod and Minltla (or Pollack, Theregra chalcogramona, nobis) ]. Just as among the egg-deposltlng forms, among Gyrodactylus there are some that are encountered only on inshore fishes [G. perlucidus Bychowsky and Poljansky from the Beldug (Ling or Quab, nobis) ] and on fishes which live far from the shore in the upper layers (G. ptertgialis Bychowsky p. 133 and Poljansky from the Pollack) or in rela- tively great depths {G. colnephorl Bogolepova from Comephorus dybowskil Corotneff). Finally certain species live on gregarious fishes (G. bychowsky! S proston from Fig. 131. Gyrodactylus rarus Wegener, diagram of reproduction. The birth of a new individual is represented by the interrupted line, the continuous line represents life of the separate individual. The last born embryo is darkened. Among worms which "gave birth" to a young individual the uterus is conditionally indicated in inflated form (middle row) just as among w^orms which still have an uncleaved egg in the uterus (right row); in nature after "giving birth" to the young indi- vidual, the uterus of the mother individual strongly deflates. 139 134 cd 3 Xi > T3 c 0) O <<-( • o CO >• rrt c T) & o o cs u u- o o O u t~i c <»-l ;-l o 3 T) T3 c CO rt 3 u ^ >v frt 4-> S- <« CJ o M-( n g crt & Ot cs CO 140 p. 135 ?5 m S! (Ml S5 t: 5S !S Q^-mJ^ a: (Z^ s> So :s § o> oo t\ tQ >»1 -^ 5-1 p) ■NJ «-l k as <>> <-rr^ s; i 4)^^,^ -» v^ Cfi to T3 o J-- a. r^ s? w^ U o> Lsi S 1 Yl o •a o o T3 T3 o c . . O rt M -a 0) U Xi 3 6 ^ c c o 4-) 0) o u o 6 & cd Q CO ••-I 141 stickelbacks) and others on solitary fishes (G. groenlandicus Levinsen from gobies). All this taken together means that the question concerning life cycles of different Gyrodactylua deserves special studies and probably will yield much that is new and interesting. In connection with the problem of life cycles^ one must pause to examine certain aspects of the question of dynamics of numbers of monogenetic trematodes. As we have already indicated (pageg'O), this question has great practical significance in addition to the theoretical one. First of all let us analyze the peculiarities of accretion in numbers under ideal conditions for egg -depositing and viviparous forms. As examples for the analysis of the given phenomena it is convenient to use the material on Dactylogyrus vastator Nybelin and Gyrodactylus elegans Nordmann from Carp. We shall attempt to show in which fashion the numbers must accrue among both types, on the condition that all the larval Dactylogyrus emerging from the eggs, or correspondingly all the individuals of Gyrodactylus which are born, survive and continue their normal existence until natural death from old age. It is understandable that this almost never occurs in nature, but such a theoretical calculation will give us much that is essential for the understanding of relations between both types of reproduction. For the estimate of the reproduction of D. vastator we take the following data (see P^g^ 108 )'■ the period of development of eggs--three days, development of larvae until maturity and first deposition of eggs --6 days, the span of life from the moment of nnaturity- - 12 days, the number of eggs deposited daily-- 5; for G. elegans (see page 131 ): the development of eggs in the uterus until the emergence of the first daughter individual- -4 days, the emergence of "remaining" embryos in sequence a day after the birth of the correspond- ing worm, the span of life of the worm from 13 to 14 days depending on the presence or absence of "remaining" embryos. Of course, all these periods are inexact and can have only an orienting oignificanceJ'or practical purposes the calculation of the accretion of numbers of both types within the limits of one month is interesting because this is the usual period of crowding of the yovmg fishes in the spawning ponds where greatest infection is possible and where occurrences of epizootics are even observed. The common scheme of accretion of the progeny from one individual D. vastator and G^ elegans is represented in Figs. 132 and 133. They are compared in such a way as to make the general character of changes apparent. Unfortunately, technical difficulties permitted us to represent the process for only 20 days. As for the remaining period the development of changes is expressed in curves of the accretion of numbers (Fig. 134 and Table 2). From these data it is apparent that the resulting figures of the changes in numbers of both types obtained almost coincide basically in spite of the connpletely different means of reproduction. Moreover, Gyrodactylus yields a greater number of progeny during the first period (up to 20 days) than Dactylogyrus . The first interesting deduction from this is that vivipa- rous Gyrodactylus potentially possess a very high tempo of reproduction 142 which is not inferior to the species which reproduce hy means of egg depo- sition, which at first glance may seem completely improbable because it is commonly accepted that viviparousness is linked with a decrease in the numbers of the progeny with the better insurance of survival. The second deduction from what has been said is that epidemic outbreaks which are observed in carp industries can be easily explained even with the presence of a weak infection in the producers which are the initial source of the in- p. 136 fection of the young ones. Finally the third conclusion from these theo- retical calculations is that the most desirable conditions in the carp indus- tries is the most rapid transfer of young fishes from the spawning ponds into the growing ponds which completely coincides with direct observations on the dynamics of the numbers of Dactylogyrus and Gyrodactylus in natural conditions. One must say that the calculations cited and the discussion about the ideal quantity of Dactylogyrus and Gyrodactylus , even though they explain certain phenomena observed in carp industries under con- siderable crowding of hosts, are nevertheless far from what exist in natural conditions. Actually the quantity of individuals depends not only on the productivity of the worms but also on a great number of external factors which, in a great majority of cases, determine the quantity of parasites. This also applies in considerable measure to the carp indus- tries, but it is more strongly expressed in nature. At the head of the factors which greatly influence the quantity of mono- genetic trematodes, one must place the means of infection, the temiperature regime of the surrounding medium, the correlations between the place of deposition among the egg -depositing forms with the place of the most frequent presence (occurrence, nobis) of the schools of the hosts and the frequency of their populations. and so forth. It is interesting to note that the question about the methods of infection of the hosts of Gyrodactylu s cannot be considered as completely solved even at the present time. As was already pointed out the repre- sentatives of this genus apparently have different life cycles, and at the samie time one must consider tentatively the considerable differences be- tween the theoretical accretion of numbers of the worms and the one which is observed in nature, as a rule, where a large number of Gyrodactylus on the body of the host, even in conditions of spawning ponds of the carp indus- try, is an exception. Consequently, the infection by these worms has certain peculiarities which prevent the survival of the majority of born individuals. Whether this is a result of the complexity of the infection of the fishes by means of adult worms or whether some other factors play a role here so far is unknown. 143 Text In conclusion let us note that the problem of dynamics of from numbers of Gyrodactylus still demands considerable work for its success- p. 137 ful solution. Without it, it is not possible to utilize fruitfully the data about life cycles for the purpose of preventing parasitic infections. 2500 eooo I5O0 1000 500 2 4 6 8 10 12 14 16 18 SD 22 24 Se 2S SO 24 -HOUR PERIODS Fig. 134. Accretion curves represent numbers of the progeny of indi- vidual Dactyloqyrus and Gyrodactylus . 1 - Gyrodactylus ; 2 - Dae tylogyrus . 144 CM W < 0) o ^1 m to O . 5 "J JrgcJcsjcM(Nlrn t— I ■— I ■— < >— I rg fi ■^ IflvDOO'-t^OvC'^ i-t i-H cvi oa CO i-HrHi-Hf— «i-Hr— If— If— * vO i— I sO ""^ vO •— ' ^H .-( fM o mH ^ bO bC (1) <0 M -u nl OQ m ^1 M-l bO 0) j:3 (1) t— 1 ■i-> i) m O • fl o o r-l •—1 < a • ^1 GO o M-l § 0) O ■!-> 1) T> M c nJ n) ■M u OD o lU ■u u iS (^ •fH m 0) o Vi (X n) V t3 o t~- (U iTl JH ■n ^1 VI o O i3 M 0) • r-l nl > ri •fH Q m C! p. 137 "< among which they have a completely different strilcture. is incepted last of any part of the armature and approximately in its final location. In the beginning it has the shape of a straight or slightly bent, transversely elongated thread, just as occurs in the early stages of the development of the connecting plate of D. longicopula Bychowsky. In a number of species, further development takes place only by means of the increase in dimensions of the supplementary plate without any change in its shape, in other plates it takes place with a change in shape and with unequal growth of separate sections of the plate. In order to avoid numerous repetitions, let us analyze the development of the complexly arranged supplementary plate in D. cornu Linstow (Fig. 146). After the formation of the plate in the shape of the curved thread, it begins to thicken and lengthen unequally in such a way that its middle part thickens much p. 146 miore than the lateral ones. As a consequence, the supplementary plate acquires the shape of an isosceles triangle with a slightly invaginated lower edge. Further, the growth develops mainly in three directions, along the angles of the triangle, as a result of which is formed an inverted T-shaped plate with slightly sharpened lateral edges and with a more blunt upper edge which grows more intensively and soon the entire upper offshoot appears with edges which are parallel or even slightly widened toward the top lateral edges and a straight-cut upper edge. Approximately during this time the lateral edges reach their final lengths and the middle of the lower one, which was initially invaginated, begins to grow intensively forming a small, more or less rounded space in the center and sonriewhat straightening the line of the lateral growth and then forming two protuberances facing downward. Continuing to grow, the top offshoot widens more and more at its free end, which is divided, forming tvvo slightly concave lobes which are characteristic of the final form of the plate. Somewhat back of the upper offshoot grow protuberances of the lower edge forming two gro'Ai;hs which are slightly narrowed to the free end and lie parallel and close to each other. In such a fashion one can notice six stages of developmient: the first, a transversely elongated straight plate, the second, a curved stick-shaped plate, the third a triangle shape, the fourth an inverted T- shaped plate with a widening of the upper stem, the fifth the appearance of stems on the lower edge and finally the form corresponding to the connecting plate of the adult D. cornu Linstow. The division into these stages is, of course, arbitrary, their number can be decreased or perhaps more easily increased. It is important, however, that the structure of similar ones among the adult individuals of a great number of species of Dactylogyrus corresponds to the enumerated stages of development of the supplementary plate of D. cornu. As an example we will cite two species of Dactylogyrus 155 which have supplementary plates corresponding to the separate stages of development in D. cornu (Fig. 146): The first stage of the development of D. cornu supplementary plate corre- sponds to the plate in 2nd to plate in 3rd to plate in 4th to plate in 5th to plate in 6th to plate in (D. cryptomeres Bychowsky (D. pulcher Bychowsky (D. varicorhini Bychowsky (D. modestus Bychowsky (D. macrocanthus Wegener (D. tuba Linstow (D. wunderi Bychowsky (D. nanus Bychowsky (D, zandti B ychowsky (D. linstowi Bychowsky (D. affinis Bychowsky (D. kulwieci Bychowsky The plan of developnnent of the connecting plate in D. cornu obviously does not appear all-embracing. The plates of certain species cannot be included in it; hov/ever, using it as a base we can easily under- stand the process of development of a supplementary plate which has a different shape as for instance among D. crucifer Wegener and D. frisii Bychowsky and_D. minor Wegener and D. chalcalburni Bychowsky. As was already indicated, D. simplicinnalleata Bychowsky, D. bicornis Malewizkaja and_D. facetus Gussew, with an aberrant form of supple- mentary plates the development of which is not clear to us, are exceptions. p. 147 Thus, we have completed the description of the separate parts of the attaching apparatus of Dactylogyrus; certain interrelations in their development still remain to be shown. The middle hooks cind the connecting and supplementary plates develop in relation to each other. One must consider it normal for the majority of the species that in the presence of stronger development of the middle hooks and their extensions, the connecting plate is more developed and the supplementary plate, where it exists at all, is more complex. This normality is a morphological expression of the functional increase in the role of the attaching armature during the attachment of the animal to its host and the mechanical fastening and the establishment of a determined size of the attaching disc. Because of this, the structure of the attaching armiature of different species must be evaluated precisely from this point of view and then the different 156 directions and ways of morphological changes become understandable. The same functional problems can be solved differently morphologically and at the expense of different parts of the attaching armature. For illustration of this condition we shall cite several examples. Among D. anchoratus (Dujardin) and the species close to it which do not have the supplementary plate, the interior extensions of the middle hooks are extremely elongated and it is they that support the upper edge of the attaching disc, strengthening and conditioning its fixed dimensions. The same problems among worms Fig. 146. Dactylogyrus cornu Linstow, the development of the supplementary plate of the attaching disc of worms from the gills of Abramis brama (L. ) from the Bay of Finland near Peterhof. Explanation in text. from the groups of D. sphyrna Linstow are solved constructionally differently, not by way of length but by a considerable widening of the interior stem of the middle hooks and, in addition to that, by the powerful development of one of the two pairs of the edge hooks which are increased twice in length and many times in width. Finally in the group of D. kulwieci Bychowsky the same role is fulfilled not by the offshoots of the middle hooks but basically by the supplementary plate which is strongly developed and almost reaches the dimensions of the middle hooks in length. Concluding the description of the development of Dactylogyrus one must say a few words about the chitinous parts of the copulatory apparatus. ' Their inception takes place at rather early stages of the development and further growth and differentiation takes place rather quickly (just as that of the entire sex system). In connection with this, the worms become mature I and first deposit eggs sometimes even before the final formation of the i attaching armature. The last circumstance has a meaning in the work on ij systematics of a given genus and sometimes leads to undesirable results i; when the stages of development of earlier known species are described as p. 148 i individual species as happened in the works of Nybelin (Nybelin, 1936) and | Alarotu (Alarotu, 1944). The duration of the development of Dactylogyrus from the free-swimming larva until adult mature individuals is very different. The most precise data were obtained by N. A. Izumova from D. vastator Nybelin (which are presented in the third chapter, page 104 ). 157 3. Development of Dogielius Bychowsky The genus Dogielius appears to be the closest to Dactylogyrus and differs from the latter mainly in the structure and location of the middle hooks of the attaching apparatus (Fig. 147). They lie in one plane surface, are oriented with their points toward each other, and at the place of the transition of the point into the base part of the hook there is a characteristic "displacement" toward the interior so that the point is sharply delineated fronn the base part. In 1936 while de- scribing the genus Dogielius (D. forceps Bychowsky) for the first time, we said on the subject: "We know that the differ- ence in the shape of the middle hooks serves as a good systematic character of a species, but in addition to that, the difference has a completely different qualitative meaning in this case. Actually, as a rule the differences lead to a larger or smaller development of certain parts, principally of the same hook. . . . Here also we have a difference connected with a change of the shape of the hook which stands independently of larger or smaller developments of the separate parts and apparently which appears during the early stages of ontogenesis. . . , and consequently, its middle hooks (Dogielius forceps Bychowsky) already differ from those in Dactylogyrus in the OJmm Fig. 147. Dogielius forceps Bychowsky, general view of the worm from the gills of Schizothorax pseudakaaiensis issykkuli Berg from the Tsku (Kazak Republic of SSSR). early stages of development. " These suppositions were fully substantiated later during the research in 1944 on a second type of Dogielius. This type (D. planus Bychowsky) was discovered by us on Schizothorax intermedius Macdelland in the river Varzob near Stalinbad; its development was studied rather completely by us with the exception of the earliest stages, as we were unable to obtain egg-laying. The youngest (known, nobis) larvae of Dogielius (Fig. 148, A) have the head end still with two lobes. The edge hooks numbering 14 are 0. 016 - 0. 017 mm in length with a well-developed terminal little hook and basal part of the handle. The later terminates in a sphere-shaped widening corresponding to the proximal part of the handle. Further growth of the 158 <1> o 1—1 (U > (0 >> CO TO rj tj cq to u 3 (U • iH H 1— < • rH (U CO •iH bO (U O J3 P O o c o o O O ^H CO C «J 0) (U bo (i 4J a C M C O o o o o o o o o o o o o rq o o o o 0) (U o o o o CM ro O O O O • • o o O IT) o o o o 4_> a) y .2 S c -3 ,, ^ - 0) MH CO ^ n, f! fl J^ •rH 43 +J O Eh W ^ a o o l-H u 0) 0£ > 3 O r— 1 •4-* nj to 1 (1) o 1 — I > (1) vO vD I^ O in CT^ Tj< in ^ — 1 (VJ (M on ro m tJh Tt< ^ O O o o O o o o o o o o o o o o o O I— I i-H I— I (\J O O O O O o o '^ in rj in o in in sO sO r- o o o o o o o r~i #— I O O l-H O I-H O CO I-H o 00 1 — I o CO I-H o CO CO I-H I-H o o • • o o • o • o • o o o o o r~- c» o o r— ( o t-H o o o o o I-H CO o ^ ro CO CO o o o o 1 1 • o I • o 1 « o • o 1 • o 1 o o 1 1 o o 00 o 00 1— t o i-H o 00 I-H o o CO o o o CO CO o o • • o o • o • o • o • o • o • • o o 00 o o o CO o^ -H O CO I-H I-H I-H o in CO CO • • o o • • o o o o o • • o o p. 149 159 1 Judging by the head end, by the structure of the edge hooks, and by the location of the middle hooks of the larva, the latter became attached to the host and lost its ciliary epithelium very recently. lateral hooks takes place rather slowly so that the middle hooks succeed in growing almost up to their final dimensions during the same period, (Table 3). The location of the edge hooks of the youngest larva is charac- p. 149 teristic: the hooks are located along the edge of the disc (with the exception of the 7th pair lying almost in the center of the disc), and the hooks of the 6th pair are separated from each other somewhat further than from the others and are oriented with their terminal hooks toward each other locating themselves in such a way and in the same place as the middle hooks will be located subsequently. The latter are already present but are located above the center of the disc (with the upper edge even extending beyond it. Fig. 148, A). As we had supposed in 1936, they already have a characteristic shape with the "displacement" between the basal part and the point. The point is already of final length but is still thin and frail, just as the base part, represented by a straight little stick two times smaller than the hook part, which is also frail and thin. The connecting plate also exists in the shape of a straight or slightly curved thread only a little shorter than the middle hooks. It lies freely between the middle hooks. Very soon after the stage described, the middle hooks descend to the lower edge of the disc, displace the 6th pair of edge little hooks laterally and cut through, thus assuming their final position. At this time, their base part is already one and one -half to two times longer than the tip of the hook (Fig. 148, C). Further development of the middle hooks of Dogielius (Fig. 149, A) takes place just as among Dactylogyrus by way of the thicken- ing of the parts which were incepted earlier and the accretion of the basal part at its free end and then the widening of the free ends and the formation of the interior and exterior extensions which almost merge and form, so to speak, a widened triangular plate. The growth of the connecting plate p. 150 (Fig. 149, B) parallels the growth of the middle hooks, reaches its final length rather slowly and begins to thicken in proportion with its final shape. The development of internal organs takes place in the same way as among Dactylogyrus. The copulatory organ (Fig. 150) is incepted at the time when formation of the widening corresponding to the extensions of the middle hooks has already begun. At first it has the shape of a thin, almost straight p. 151 pipe with a weakly developed base from which departs the supporting appa- ratus in the shape of a band with a small widening in its upper third and with a sharpened free end. Further growth takes place rather quickly by way the shape of an increase in the volume and size of the pipe and of the base and of the growth and complexity of the terrainal and of the supporting apparatus. The copulatory organ acquires its final forna at the same time as the termination of the growth of the parts of the attaching armature. 160 OOlUM Fig. 148. Dogielius planus Bychowsky, larvae from the gills of Schizo- thorax intermedius McCL from the river Varzob (Tadjikistan, SSSR). A--General view of a larva which has just settled on the gills; B--General view of a more fully grown larva; C--Attaching armature of a more mature larva. Fig. 149. Dogielius planus Bychowsky, stages of development of the attaching apparatus from the gills of Schizothorax intermedius McCl. from the river Varzob (Tadjikistan, SSR). A--Stages of development of middle hooks; B- -Stages of Development of the connecting plate of the middle hooks. 161 (LDlMM Fig. 150. Dogielius planus Bychowsky, stages of development of the copulatory organ of the worms from the gills of Schizothorax intermedius McCl. from the River Varzob (Tadjikistan, SSSR). 4. The developraent of Ancyrocephalus Creplin We accept the genus Ancyrocephalus in thebroad sense in the present work. The reason for this appears to be the extremely formal approach of Anierican researchers toward the description of new genera of Ancyrocephalinae and the lack of the opportunity to conduct a special revision of this interesting group at the present time. Undoubtedly, how- ever, considered in such scope this genus is artificial and demands sub- division. It seems to us that from Ancyrocephalus (s. lat. ) one can isolate several independent groups (apparently the actual genera), on one hanu, the group of forms with the type of the genus, Anc. paradoxus Creplin, which have intestinal trunks not merging with each other, and on the other hand, the second group of species with merging intestinal trunks to which are related first of all well-known types; Anc . cruciatus (Wedl. ), Anc. vanbenedeni Parona and Perugia (for more details see the chapter, "A System of Monogenetic Trematodes" pages 348-352), The genus Ancyrocephalus (£. lat.) basically resembles Dactylogyrus Diesing in its structure but differs by the presence of four middle hooks on the attaching disc, each pair of which is connected by a special plate. The disc doesn't bear any supplementary chitinous for- mations. Both connecting plates are more or less of a simple form and never articulate with each other. The edge hooks are ordinary and number 14. In connection with the above-mentioned understanding of the genus the description of the development is given according to repre- sentative species, because generalized data can subsequently lead to faulty representations concerning the systematics of the group. Certain considerations of general order are expressed at the end of the section. 162 Ancyrocephalus paradoxus Creplin--During our work at Saratov in July 1947 we succeeded in hatching a free-swimming larva of Anc. para- doxus. Creplin from the eggs of the parasite from the gills of Sandre [ L/Ucioperca lucioperca (L. )] . The development of the larva in the egg D, 152 took place in four days at temperatures of 20 to 24°. The larva which had emerged from the egg had a length of about 0. 15 mm with a width of about 0. 05 mm (the egg having the length of about 0. 10 and the width of about 0.06 mm). The mature adult worm has an average length of about 2 mm, i.e., 13-14 times longer than the larva. The latter have a ciliary epi- thelium located in essentially the same fashion as among the larvae of Dactylogyrus, i.e. , in three zones or belts. The attaching disc of the larva is not at all delineated from the body and is equipped with 14 edge hooks beside which there are no traces of chitinous formations so that the inception of the middle hooks takes place later. The edge hooks have the length of about 0.015- 0.018 mm; their hooked part is well-developed but the handle is weak with a small widening at its free end (Fig. 151). Among adult worms (Fig. 152) the edge hooks have the length of about O.OIkm, Fig. 151. Ancyrocephalus paradoxus Creplin, attaching armature of the free -swimming larva. 0.0l6to 0.019 mm, i.e., they are almost completely of the same sizes as in the larva. Judging from the observations on live mature worms, their edge hooks hardly function whereas among the young forms, which have fully formed middle hooks, the edge hooks still function fairly actively. The larvae have two pairs of relatively large eyes. The internal structure of the larva is completely analogous to that of the larva of Dactylogyrus. Further development has not been followed through. The youngest known individuals from the hosts which were at our disposal are about 0, 5 mm in length and already have fully formed attaching and sex armatures. Fig. 152. Ancyrocephalus para - doxus Creplin, adult worm from the gills of Lucioperca lucioperca from Ahchtarin estuaries (Sea of Azov). 163 Ancyrocephalus (s. lat. ) cruciatus (Wedl. )--We also know only the structure of the free-swimming larva of Anc. cruciatus (Wedl.). It was obtained by us seven days after the deposition of the eggs by the worm, from the gills of the Viun [ Misgurnis fossilis (L. )] , in June 1938 (at the Peterhof Institute of Natural Science hear Leningrad). The larva is 0. IZ mm in length and has a width of 0. 03 nrun. The head end has weakly ex- j^^j pressed lobes. Two pairs of eyes are strongly developed. The ciliary epithelium is located in the same fashion as it is in A. paradoxus Creplin, The attaching disc is weakly expressed. On it are located 14 edge hooks (Fig. 153) of the usual dactylogyrid form, about 0.017 - 0.018 mm in length and with the length of the terminal hook about 0.006 mm. These dimensions re- main without change also among adult worms. The first pair of middle hooks in the shape of plates of about 0. 020 mm in length which are slightly curved and sharpened on the lower end, already Fig. 153. Ancyroce- lies in the center of the attaching disc phalus (s_. lat. ) cruciatus along with the edge hooks. Besides that, Wedl, attaching arma- a slightly curved very tender connecting ture of a free -swimming plate of the first pair of middle hooks larva, lies freely between them. It is about 0. 008 mm in length. There are no traces of the second pair of middle hooks or of their connecting plate. In such a fashion we see a different development in time of the middle hooks in Anc . cruciatus (Wedl. ), and the inception of the first pair takes place even during the embryonic development considerably earlier than the appearance of the traces of the second pair. As is known, the adult Anc. cruciatus (Wedl. ) (Fig. 154) has a structure of the middle hooks and of the connecting plates similar to that of Dactylogyrus and also a similar inner organization, so that one can easily visualize, in generalcharacter the pro.cjress of further develop- ment with the exception of the correspondence of stages of development of separate parts in time. In connection with the latter, one can indicate that the growth of the first pair of middle hooks continues after the in- ception of the second pair, for we observed young immature worms with underdeveloped hooks on both pairs. Ancyrocephalus (s. lat. ) vanbenedeni (Parona and Perugia)-- During the work at Karadaga Biological Station in August of 1957 we hatched the larva of A. vanbenedeni several times. The period of develop- ment in all instances was about 4 days. The larvae which emerged from the eggs had a length of about 0. 075 mm with a width of about 0. 025 mm. The larva (Fig. 155) is torpedo-shaped with a powerfully developed "little tail" at the posterior end. The ciliary epithelium is distributed in three zones just as among the preceding species. The attaching disc has 14 edge hooks; no traces were discovered of the middle hooks in the process ^^^ of inception. The edge hooks are of identical shape with a weakly 164 expressed handle; their length is very insignificant- -about 0. 01 mm. Among adult forms the sizes of the edge hooks are the same and conse- quently no growth is observed among the latter in the'post-embryonic period. Further development has not been followed through. The middle hooks of adult worms are more or less of the same sizes (Fig. 156); apparently the ventral pair is in- cepted first. In spite of the fact that this species is encountered both in marine and fresh water the develop- ment of the eggs ap- parently takes place only in sea water, for our attempts to obtain larvae in fresh water were not successful. afl/M" Fig. 155. Ancyroce- phalus (s.lat.) vanbenedeni (Parona and Perugia), free- swimming larva. Fig. 154. Ancyrocephalus (s. lat. ) cruciatus Wedl. , adult worm from the gills of Misgurnus fossilis(L,. ) from the region of Peterhof (Leningrad region). at an air temperature Ancyrocephalus (s. lat. ) mogurndae (Yamaguti). Certain data concerning the development of this species, discovered in Lake Hanka in 1948-1949 on the gills of Sineperca chua-tsi (Bas. ) are reproduced in the works of A. V. Gussew (1955). He writes: "The development continued about 3 days (65 hours) on the first day of about 27° centigrade, the second--2lO to 26°, and the third--180 to 22°. The larva has a length of about 0. 06 and a width of about 0.02 mm, it has 4 little eyes with little lenses, is equipped with three zones of cilia, on the anterior end, along the sides of the equatorial region and on the posterior (the latter is some- what displaced toward the dorsal side). The attaching disc is closed. Its armature (Fig. 157--B. B. ) consists of 7 pairs of edge hooks with lengths of about 0.015 - 0. 017 mm. There are no traces of the middle hooks. " In addition to that A. V. Gussew indicates that, "that on the gills of the perch-bass ( Sineperca --B.B. ) one immature individual with a length of 0. 34 rmn and a width of 0. 09 mm and with fully developed middle hooks which have the same common length--0, 048 mm and the point 0. 019 rnm- was found. The ventral connecting plate is still tender, 0. 005 x 0. 042 mm. The dorsal connecting plate is very thin and apparently is incepted after the ventral one during the development (just as the dorsal hooks), its sizes are 0. 002 x 0. 055 mm. The copulatory organ and the vaginal armature 165 begin to form in the shape of thread-like pipes and three plates corre- sponding to the terminal part of the supporting apparatus. " The adult wornns (Fig. 158) have edge hooks 0. 015 - 0. 019 mm in length and thus one can consider that no growth is observed among edge hooks of this species, just as among the preceding ones. OMtMM Fig. 156. Ancyrocephalus (s.lat.) vanbenedeni (Parona and Perugia), attaching armature of the disc of an adult worm from the gills of Mugil auratus Risso from the region of Karadaga (Black Sea). Fig. 157. Ancyrocephalus (s.lat.) mogurndae (Yamaguti), attaching armature of a free -swimming larva. (According to Gussew, 1955). Ancyrocephalus (s. lat. ) curtus Akme row.- -This worm de- scribed from the Reservoir of Amur from Percottus glehni (Dyb. ) was studied by A. V. Gussew in 1948 - 1949 in Lake Hanka. He hatched nnany larvae and the period of developnnent of their eggs was about 5 days. The length of the larva was about 0. 09 rnm and the width 0. 03 mm. Their structure is typical: they have three zones of ciliary covering; their intestine is circular with a large pharynx. The armature of the attaching disc (Fig. 159) consists of 14 edge hooks--0. 015 to . 017 mm in length and a pair of chitinous thin brackets (embryonic inceptions of the ventral pair of middle hooks) about 0. 016 mm in length. In addition to this, A. V. Gussew once found an immature young worm which still possessed undeveloped dorsal middle hooks and their connecting plate, while having fully fornned ventral hooks and their plate. Adult worms (Fig. 160) have edge hooks 0. 016 - 0. 020 mm in Length, that is they grow somewhat in the postembryonic period. This growth proceeds by way of an increase of the round terminal part of the handle which is developed more weakly annong young worms. D. 155 Ancyrocephalus (s. lat. ) pavlovskyi Gussew--In 1948-1949 A. V. Gussew obtained larvae of this species on Lake Hanka. The develop- ment of the eggs continued about 4 days. The larva has three zones of cilia the first- -of eight cells, an equatorial --along the sides of the body of 4 (6?) ciliary cells, and a posterior one (the quantity of the cells has not been determined). The attaching disc (Fig. 161) with 7 pairs of edge hooks 0. 013 - 0.016 mm in length and a pair of powerful sabre - shaped inceptions of the ventral middle hooks of about 0, 02 mm in length. p. 156 166 Ancyrocephalus (s. lat. ) hemibarbi Achmerow--The larvae of this species were obtained by A. V. Gussew of Lake Hanka in 1948-1949. The embryonic development (in hanging drops) required 4 to 5 days. The larva has three zones of cilia. The attaching disc is equipped with 7 pairs of p. 157 ^OBIhm' Fig. 158. Ancyrocephalus (s. lat.) mogurndae (Yamaguti), attaching armature of the disc of an adult worm from the gills of Siniperca chua-tsi (Bas. ) from the Island of Hanka. (WImm Fig. 159. Ancyrocephalus (s. lat. ) curtus Achmerow, attaching armature of a free-swimming larva. (According to Gussew, 1955). edge hooks, 0. 012 to 0. 014 mim in length and one pair of powerful sabre- shaped inceptions of the ventral middle hooks (Fig. 163); the length of the latter is about 0. 025 mm. The adult worms, which parasitize the same fishes as the preceding type, have the usual attaching arnnature (Fig. 164). Fig. 160. Ancyrocephalus (s. lat. ) pavlovskyi Gussew, attaching arma- ture of the disc of an adult worm. (According to Gussew, 1953). The edge hooks are also of two types^ however, the difference between them is considerably less than among A. pavlovskyi Gussew. Thus there are only two small hookS; the 6th pair. Their length is 0.016 to 0.018 mm. All the remaining hooks have a length of 0. 025 to 0. 039 mm (the smallest among them is the 7th pair). 167 Thus, from the existing incomplete material on the develop- ment, more precisely according to the larvae, it is apparent that in Ancyrocephalus the situation is much more complex than among the pre- ceding types. Thus, from the seven species which have been examined. 0.01 HM 001mm Fig. 161. Ancyrocephalus (s. lat. ) Fig. 162. Ancyrocephalus {s. lat. ) pavlovskyi Gussew, attaching armature of the free -swimming larva. (According to Gussew, 1955). pavlovskyi Gussew, attaching armature of the disc of an adult worm from the gills of Hemibarbus maculatus Bl. (According to Gussew, 1955). on three the middle hooks are incepted in the postembryonic period, whereas among five (sic) species the inceptions of the first pair of middle hooks are already formed at that time. In one species the connecting plate of the ventral (first, pair) of the middle hooks is also incepted in the embryonic period. The fate of the edge hooks also varies. Among 4 species they remain ^ ^ without change during the ^^^\^ entire life of the worms, whereas, among three species DO 1mm Fig. 163. Ancyrocephalus (s. lat.) hemibarbi Achmerow, attaching armature of a free- swimming larva. (According to Gussew, 1955). Fig. 164. Ancyrocephalus (s. lat.) hemibarbi Achmerow attaching arma- ture of the disc of an adult worm from the gills of Hemibarbis maculatus Bl. (According to Gussew, 1955). they grow more or less intensively during the postembryonic period. It is impossible not to note that among forms which have hooks which do not grow, in a majority (among 3 out of 4), the middle hooks are incepted 168 1 0) >^ o.^ ^ o -a CO ,— 1 — 1 ^ ^ I e J3 nJ m o (U 0) 0) TJ o •i u -^ £ > C •i-i f-l 0. CL, o ^ J3 1— 1 1) O tages show CO o ■u d o >^ .— < CD +^ ^ • r-t CO • u lU c d I— * Ofl c V( 0) 0) O d f— * CO :S S • t-H o u C VM 4J u ^ , n! V CO >^ -d m r— 1 O o P. n w "—^ •f-* • *-< 00 ^1 o ti. f—l o o p. 158 d o • r-i nl u (t1 a n 1-1 XI >^ M ^ Tl u o M u ^ nJ +j (-• VH I— 1 d c '-' (U nj x> •f-i ■4-1 u u r—t 0) m y, the just s .1-1 CD 1 — I c\5 o 1—* 1 CO vO 00 nJ m ^ t-! O d XI 1— 1 d .—I n1 o d 1— < •f-t 00 , d ^ o 00 ^^ 0) §• t— I « at CD OS O X) o cq o to d I— ( • (^ (U ,d •I-* 0. d 0) • H o d h >> o o d 3 nJ nJ ■!-> 1— t O a, ^4 a • 00 vO ■—1 • on .1-1 fn 169 during the postembryonic period. This can scarcely be a pure coinci- dence. In conclusion one must say that the system of the Ancyrocephalinae as a whole demands a rather substantial and careful revision, and that the first priority should be given to the study of the species, which are so far classified by us in the genus Ancyrocephalus. 5. The development of Protancyrocephalus Bychowsky During our work on South Sakhalin in 1946 and on the Island of Shikotan in 1949^ we studied the development of a new species and genus of Ancyrocephalinae — Protancyrocephalus strelkowi Bychowsky parasitizing the gills of young flounders, Lemanda aspera (Pallas). The absence of connecting plates between the two pairs of middle hooks appears to be a characteristic trait (of this species, nobis). The basic traits of organi- zation are clear from the drawing of the adult form. The development of Pr. strelkowi from the moment of egg- deposition to the emergence of the free -swimming larva takes place during 8 to H days at average temperatures of 18° to 20°. The free- swimming larva of this type has a length of 0. 08 - 0. 10 mm, it has a relatively blunt anterior end and an elongated and sharpened posterior end (Fig. 165). The ciliary covering is distributed just as it is annong the larvae of Dactylogyrus, but both anterior groups do not merge at their anterior ends, whereas the third group consists of tw^o clearly divided sections of ciliary epithelium lying along the sides of a special cone which is more sharply expressed than in Dactylogyrus and falls off at the same time as the ciliary epithelium. The attaching disc js already delineated from the body at the time of emergence of the larva from the egg, but the 14 edge hooks have not yet cut through at this time and lie with their points oriented toward the center of the disc. Their length is about 0. 015 mm with terminal little hooks about 0. 005 mm. There are two groups of head glands and four well-developed pigmented eyes in the free -swimming larva just as in the adult aninaal. The digestive system is of the customary type with a large pharynx and circular intestine. The nervous system is almost invisible with the exception of the more noticeable heau ganglia located at the level of the eyes. The excretory system is unnoticeable. The development of edge hooks takes place as usual, p. 159 their growth is insignificant because among fully matured egg -laying indi- viduals the edge hooks have a length of not more than 0. 018 - 0. 020 mm. The larvae which have just settled on the gills have 4 large transparent 1 We observed the settling of the larva on the gills during the entire time of study (July-September): however, in the Bay of Anam on the Island of Shikotan this process was of more concentrated nature (occurring, nobis) at the end of July --beginning of August. In our diary it is noted that the 170 entire mass of larvae which were found at this tinne on the fishes were in absolutely the same stage of development. Thus, the deposition of eggs among these forms takes place extremely rapidly (see chapter on life cycles, page 111). cells in the interior of the body somewhat above the attaching disc which apparently play a role in the formation of the middle hooks. The latter are incepted in their places alnnost simultaneously and descend to the disc together (Fig. 167). However, certain differences are observed in the tempo of their growth: the first pair grows somewhat faster and among the mature animals it was slightly but distinctly larger than the second pair. The nature and the sequence of the development of middle hooks are the same as among Dactylogyrus (Fig. 168). The copulatory organ is incepted in the shape of a pipe of almost the same shape and size as among adult animals but with a weakly developed base which grows rather slowly (Fig. 169). The time of inception of the copulatory organ coincides with the beginning of the fornnation of the extensions of the second pair of middle hooks. 6. The development of Ancylodiscoides Yamaguti The genus Ancylodiscoides (Fig. 65), established in 1937 by Yamaguti, pertains to Ancyrocephalinae and is characterized mainly by the structure of the attaching apparatus, which consists of 14 very small edge hooks and 2 pairs of middle hooks. The latter are of different sizes and the interior offshoots of the large pair are equipped with supplementary plates articulating with them (Fig. 170). There are four eyes. The in- testinal trunks merge at the posterior end. The sex system (is equipped, nobis) with a strongly developed chitinous copulatory organ and vaginal pipe (the latter is sometimes absent). They parasitize Siluridae and Bagridae. At the present time there is a number of materials (papers, nobis) about the development of the representatives of aoiHM VV I ' h ^^^^ genus. Thus Siwak (Siwak, 1932) in a work dedicated to the description Fig. 169. Protancyrocephalus of A. vistulensis Siwak from the gills strelkowi Bychowsky, stages of the European Silurus reproduces a of development of the copu- drawing of a free-swimming larva of latory organ. Explanation in this type and presents his observations text. on the development and further growth of the larvae. A. V. Gussew in 1948- 1949 hatched the free -swimming larvae of A. strelkowi Ackmerow and A. varicus Ackmerow. Finally, during our work in the Delta of the Volga in July, 1932 we sketched one of the later stages of development of ^ siluri // 171 Zandt and in August, 1953^ we also hatched larvae of this type, and pre- sumably A. vistulensis Siwak and observed a number of subsequent stages of their development. The development of the eggs of Ancylodiscoides takes place in from 3 to 6 days depending upon temperature. The larva which has just emerged from the egg (Fig. 171) is of the same shape and structure in all species as the larvae of Dactylogyrus, but differs in the fact that its attaching armature (Fig. 172) has two middle hooks in addition to the edge hooks (14 and not 12 as Siwak erroneously indicates). The Fig. 170. Ancylodiscoides siluri latter are incepted above the edge (Zandt), middle hooks of the disc hooks in the shape of chitinous of the adult worm from the gills little parentheses just as takes place of Silurus glanis L. from the anaong Anchyrocephalus (s^. lat. ) Delta of the Volga. cruciatus Wedl. but in opposition to the latter, the connecting plate of this pair is as yet absent, it is incepted later. p. 160 Fig. 171. Ancylodiscoides sp. sp. free-swimjning larvae, A- -A. vistulensis (Siwak), the larva is enlarged 400 times (According to Siwak, 1932); B--A. siluri (Zandt); C--A. strelkowi Ackmerow. 172 The sizes of the larvae: A. vistulensis - -according to our preparations the length is 0. 06 - 0. 08 mm and the width is 0. 02 - 0. 04 rnm and correspondingly 0. 11 and 0. 04 mm, according to the data of Siwak; the length of the edge hooks is 0. 015 - 0. 016 mm and the inceptions of the middle hooks 0, 016 - 0. 019 mm; in A^ siluri the length is 0. 05 - 0. 08 mm and the width is 0. 02 - 0. 04 mm and the length of the edge hooks is the same as in the preceding species and the length of the middle hooks is 0. 022 - 0. 026 mm; A, strelkowi - -length up to 0. 15 mm, the width being 0. 03 mm, the length of the edge hooks 0. 013 - 0. 015 mm and the inceptions of the middle hooks 0. 012 mm; A. varicus --the length and the width of the larva has not been established by A. V. Gussew, the length of the edge hooks is 0. 013 - 0. 015 mm and of the inceptions of the middle ones 0. 015 mm. p. 161 Fig. 172, Ancylodiscoides sp. sp. attaching armature of the free-swimming larvae. A--A. siluri (Zandt); B--A. strelkowi Achmerow. The edge hooks among representatives of this genus apparently either do not grow completely or almost completely and retain their embryonic traits. Siwak indicates that during the further development of the larva of A. vistulensis the first pair of middle hooks reaches con- siderable length and is already equipped with a connecting plate when the second pair is incepted. At that time the larva reaches 0,15 mm in length, the first pair reaches final sizes when the larva is 0. 23 mm long whereas the second pair develops in full toward the time of the cessation of the growth of the worm (length 0. 74 - 1. 14 mm). According to our obser- vations on A. vistulensis, which in general are similar to the data of Siwak, the first pair of middle hooks and their connecting plate reach the final stage of their development before the inception of the second pair (Fig. 173, A). The latter is incepted in the shape of two slightly curved little parentheses above the attaching disc (Fig. 173, B) and reaches rather large sizes before the second connecting plate begins to form. The supplementary plates are incepted last. The chitinous arma- ture of the sex system has already begun to form about that time. p. 162 The development of A. siluri takes place in a similar fashion to that of A. vistulensis. Apparently during the early stages the difference is expressed only in the sizes of the body and the chitinoxis parts of the attaching disc. However, during later stages among A. siluri 173 one observes a certain delay in the inception of subsequent elements along with a larger size of hooks. Thus, middle hooks of the first pair reach RDIhh aoifM Fig. 173. Ancylodiscoides sp. sp., attaching armature of a developing larvae from the gills of Silurus glanis L. frona the Delta of the Volga. Explanation in the text. considerable size (Fig. 173, C), where- as the inceptions of their connecting plate is not yet observed. Later, even though the first pair of middle hooks and their plate are fully formed the inception of the second pair will still not be observed for a long time (Fig. 173, D). After the inception of the second pair of middle hooks the larva grows rather slowly. During that time the larva (Fig. 174) has a length of about 0. 23 mm and a width of 0.08 mm (in a somewhat compressed condition). The edge hooks are of final shapes and sizes (0.015 - 0.017 mm, i.e., they have grown scarcely noticeably) --the first pair of the middle hooks is of the customary shape for the adult worm; its sizes: length 0. 024 mm, the basal part 0. 022 mm, the interior offshoot 0. 009 mm, the exterior 0. 003 mm and the edge or point U. Ui3 mm. The connecting plate is fully developed, its length is 0. 040 mm. Above the attaching disc lie two middle hooks in the shape of parallel parentheses which are curved at the upper end and Fig. 174. Ancylodiscoides siluri Zandt, the larvae with the recently formed second pair of middle hooks on the atUching disc from the gills of Siluris glanis L. from the Delta of the Volga. 174 sharpened in the lower part, and which have a length (along the curve) of about 0. 040 mm. There are no traces of the connecting plate of the second pair. The eye spots are of the usual form and location. The digestive system has a rounded pharynx, 0. 02 mm in diameter, and circular in- testine without traces of the posterior blind growth characteristic of the A. siluri. There aren't any traces as yet of the sex armature. Subsequent development has not been followed through, but its progress is evident. All in all, one can note that the development of representatives of Ancyclodiscoides is close to that of Ancyrocephalus which has larvae with the inceptions of middle hooks and differs sharply from the develop- ment of Protancyrocephalus among which the process of formation of the middle hooks proceeds simultaneously. 7. The development of Bychowskyella Achmerow The genus Bychowskyella, described in 1952 from Amur Bagridae by A. H. Achmerow, resenables Ancylodiscoides in its structure, but is easily distinguished by its peculiar armature of the attaching disc (Fig. 175). The latter carries two pairs of middle hooks of different size, Fig. 175. Bychowskyella pseudobagri Achmerow, attaching armature of an adult worm from the gills of Pseudo— bagrus fulvidraco (Rich. ) from the Island of Hanka. Fig. 176. Bychowskyella pseudo — bagri Achmerow, free-swimming larva. 175 one unpaired connecting plate (of the second pair of middle hooks), two connecting plates of the first pair of middle hooks and a pair of supple- mentary plates, articulating with the body of the second pair of middle p. 163 hooks; the edge hooks are of two types; 4 pairs of small ones which pre- serve embryonic shapes and sizes and three pairs of large ones with massive handles. A. V. Gussew in his work on Monogenoidea of the fishes of L,ake Hanka (1955) describes a free-swimming larva in one of the latter stages of development of B. pseudobagri Achmerow. The development in the eggs takes place in four days at temperatures of 16 - 21°, The larva which has just emerged from the egg is torpedo- shaped with 3 zones of cilia located just as among Dactylogyrus (Fig. 176). Gussew succeeded in counting, approximately, the number of cells in each of the ciliary zones. Thus, the first zone consists of 9 + 9 (the very p. 164 anterior end of the body of the larva is free of ciliary cells), the middle of 6 + 6 (can be 7 + 7) and finally the posterior, unpaired and lying in the shape of a little cap on the dorsal side behind the disc --of 12(?) ciliary cells. The larva (is equipped, nobis) with 4 well-developed eyes. The attaching disc (Fig. 177) is equipped only with 7 pairs of edge hooks, 0. 013 - 0.017 mm in length. There are no traces of other armature. In addition to that, Gussew writes in his work: "Besides the mature worms we found one young specimen of this type in which the ventral middle hooks (the first pair according to our ternninology--B. B. ) were almost formed (their length is 0. 027 min, the length of the point is 0. 013 mm), their connecting plates are yet without articulated little heads (their length is 0. 027, their D.DIhh Fig. 177. Bychowskyella pseudo - bagri Achmerow, attaching arma- ture of a free -swimming larva. I10IHM_ Fig. 178. Bychowskyella pseudo- bagri Achmerow, attaching arma- ture of the young worm in the pro- cess of development. Pseudobagrus fulvidraco (Rich. ). (According to Gussew, 1955). thickness is 0.003 mm), the dorsal middle hooks (second pair--B.B. ) are as yet without a body, and are represented only by the point and its narrowed part, whereas their connecting plate is in the shape of a tender. 176 V-shaped, curved chitinous membrane and finally large edge hooks already forming handles" (see Fig. 178). Consequently we see that the development of Bychowskyella takes place in the same fashion as among Ancylodiscoides Yamaguti with the exceptions of differences in the development of the edge hooks. 8, The development of Heteronchocleidus Bychowsky Heteronchocleidus buschkieli Bychowsky (Fig. 118), which was studied by us from aquarium fishes, is a representative of curious tropical monogenetic trematodes, which are related to the family Dactylogyridae O.OIhm Fig. 179. Heteronchocleidus buschkielli Bychowsky, attaching armature of the disc of an adult worm from the gills of little aquarium fish Macropodus opercularis (L, ) Leningrad. Fig. 180. Heteroncho- cleidus buschkielli Bychowsky, free- swimming larva. (Ancyrocephalinae), parasitizing Anabantldae. The internal structure is of the usual type for this family, the presence in the adult stage of three fully developed middle hooks and one (hook, nobis) which is very retarded in development, and many times smaller in size than the rest (Fig. 179) is characteristic for them. The embryonic develop- ment takes place within 5 to 6 days. The free -swimming larva of H. buschkieli (Fig. 180) corresponds to that of representatives of the genus Ancyclodiscoides. Its length is about 0. 07 mm and its width is 0. 02- 0.03 mim. The ciliary covering consists of a zone divided into two groups with a weakly developed middle and a larger undivided third. The larva has 14 very tender edge hooks on its disc which are about 0. 009 rnm in length. In addition, somewhat above them, lies the first pair of middle hooks in the shape of slightly curved little parentheses of slightly greater length than the lateral hooks (0. 009 - 0. Oil mm) (they are not expressed on the drawing because of their unusual frailty). The connecting plate of the first pair and the second pair of middle hooks are still absent. The p. 165 177 development of the attached larva apparently proceeds in the usual way (unfortunately this has not been fully studied). It is known only that one hook of the first pair of middle hooks does not grow at all in the post- embryonic period. During the early stages of development this hook (during the observation on live worms) acts completely normally and serves, just as the one corresponding to it, for the attachment of the larva^ whereas among adult individuals it doesn't play any role whatsoever. 0.01mm 9. The development of Diplectanum Diesing As is known, the genus Diplectanum (Fig. 14) is characterized by the presence of a more complex attaching arnaature than among all the previous genera. The attaching apparatus (Fig. 56) consists of 14 lateral hooks, 2 pairs of middle hooks, 3 connecting plates -- one unpaired middle and 2 paired, articulated with the middle hooks, and finally of 2 peculiar supple- mentary discs, all deployed on the disc. These discs (whence comes the name of the genus) lie on the upper edge of the attaching disc one on the ventral and one on the dorsal side and are equipped with a large number of small chitinous stick-shaped fornnations with hook-shaped offshoots located in regular rows (Fig. 181). The develop- ment of the genus unfor- tunately has not been studied; known are only the free- swimming larvae of D, aculeatum Parona and Fig. 181. Diplectantim aculeatum Parona and Perugia, chitinous armature "plectans" of an adult worms from the gills of Corvina nigra Cuv. and Val. from the region of Karadaga (Black Sea). On the left is one row, greatly magnified. Perugia and D. similis Bychowsky, a new species which is very close to the first species ajad of which we collected a large number of individuals in June 1935 at the Sebastopol Biological Station and in July -August 1949 at the Karadaga Biological Station from the eggs deposited by worms on the Gorbil ( Corvina nigra Cuv. and Val.) (Humpback Salmon, nobis) . These larvae resemble those of the genus Dactylogyrus but deserve detailed description. The free -swimming larvae (Fig. 182) which have just emerged frona the egg have an elongated, torpedo-shaped form with blunt anterior ends and a very sharpened posterior end. At the anterior 166 178 end of the larva there is a small, rather mobile nose -shaped growth, and approximately at the end of the second third of the body, there are small indentations which delineate the weakly differentiated attaching disc. In D. aculeatum Parona and Perugia the length of the larva (in the straightened condition) is 0. 07 to 0. 10 mm, whereas the width is 0. 03 - 0. 04 mm and among D. similis Bychowsky the length is 0. 06 - 0. 8 mm and the width is 0. 03 - 0. 35 mm. The ciliary covering consists of three zones. Its anterior zone is located on the head end and extends posteriorly to the level of the anterior pair of eye spots. It is divided by the nose-shaped growth into two lateral groups of cells and on the ventral side they are closely separated from each other, whereas on the dorsal side they merge at the middle line of the body. The second zone of ciliary epithelium is located along the sides of the body in two parts, which extend posteriorly from the level of the pharynx to the anterior edge of the attaching disc. Both groups of this zone extend to the ventral and dorsal sides of the body but do not touch aoiHM Fig. 182. Diplectanum silimis Bychowsky, free -swimming larvae. each other. The third zone, consisting of two groups merging with each other, is located behind the attaching disc on a cone-shaped growth of considerable diinensions (among both species about 0.008 - 0.012 x 0.012 - 0. 015 mm). This growth is exceedingly mobile and serves in some measure for the regulation of the direction of the motion of the larva. This cone is completely discarded as a unit with the shedding of the ciliary epithelium when the larva becomes attached to the host. The larva carries two groups of glands with well-developed ducts at the head end. There are two pairs of large eyes (the anterior are somewhat smaller) with large light-refracting lenses facing outside from the pigmented spot. The pharynx lies behind the eyes, it is round and about 0. 015 mm in diameter; the intestine is sac-shaped, weakly developed and poorly noticeable. During the study of live subjects one can observe the lateral trunks of the excretory system which give off numerous outgrOAvths and form a number of anastomoses. Betrween the eyes and the anterior end of the pharynx two transversal canals depart from the lateral trunks of the excretory system. These canals merge in the middle and proceed toward the an- terior end where they separate dichotomously. It has not been possible 179 to ascertain the number of flame cells; however, it can be said that their number is considerably larger than 20. The sizes of these cells are about 0. 005 mm. The attaching disc is sharply delineated from the rest of the body and is somewhat smaller in width. The armature of the disc consists of 14 edge hooks of the usual shape for Dactylogyridae with a length of about 0. 012 mm among D. aculeatum and about 0. 008 mm among D. similis. In such a fashion, all four middle hooks, three connecting plates, and both attaching plates are incepted and developed already after the attachment of the larvae to its host. p. 167 10. The development of Lamellodiscus Johnston and Tiegs The genus Lamellodiscus (Fig. 34) is very close to Diplec - tanum Diesing and differs mainly in that its supplementary discs carry not a number of stick-shaped formations but a number of concentrically disposed chitinous threads (Fig. 183). During our work at the Karadaga Biological Station in July-August, 1947 we obtained free-swimming larvae of two species (L. elegans Bychowsky, and L. fraternus Bychowsky) and studied the development of one of them more in detail. The material for this w^ork was collected from the gills of Sargus annularis (L. ). The free-swimming larvae of both species emerge from the eggs three or four days after the deposition of the latter by the mother individual. The larvae are torpedo-shaped just as the larvae of Fig. 183. Lamellodiscus elegans Bychowsky, middle hooks, their connecting apparatus and chitinous armature of the supplementary discs of an adult worm from Sargus annularis (L. ) from the region of Karadaga (Black Sea). Diplectantim which they greatly resemble both in exterior shape and in- terior structure (Fig. 184). The sizes of the larvae of both species are the same: their length is about 0. 09 mm with a width of 0. 03 mm (the 180 greatest width is at the level of the first or second pair of eyes); the attaching disc is almost rovuid, about 0. 025 — 0. 028 mm across; the dimensions of the pharynx are about 0. 01 - 0. 008 mm. The attaching armature consists of 14 edge hooks 0. 008 - 0. Oil mm in length. The ciliary epithelium of the larva is cast off at different times. One can often observe the settled larvae with a part of the ciliary cells which have been retained. The latter fall off in groups, at first on the attaching disc and the anterior end of the body. The cone-shaped growth, on which the third zone of cilia is located, falls off as a unit as is evident from Figure 184. 001mm, Fig. 184. Lamellodiscus fraternus Bychowsky, free- swimming larva casting off the cone of the ciliary zone of the posterior end. :j H^ «/;/«« O.OlHH Fig. 185. Lamellodiscus elegans Bychowsky, attaching armature of the disc of the larva in the process of development from the gills of Sargus annularis (L. ) from the region of Karadaga (Black Sea). Explanation in text. p. 168 Strange as it may seem the larvae which have just settled are somewhat snnaller in size in comparison with the free -swimming stage. Thus, the youngest larvae which are discovered on the gills of the host, have the length of 0. 06 - 0. 07 mm and a width of 0. 025 - 0. 035 mm. They begin to feed very quickly and their attaching disc acquires the trans- versly elongated shape characteristic for the genus. The edge hooks stop growing completely and retain their initial sizes during the entire life of the worms. The middle hooks begin to form alnnost simultaneously and grow quickly. At first they have the shape of weakly curved plates of the same width for their entire length with a sharply bent and sharpened lower end--the point of the hook (Fig. 185, A). Somewhat after the in- ception of the middle hooks the central connecting piece appears in the form of a straight or slightly curved and hardly noticeable little plate (Fig. 185, B). 181 The disposition on the disc of these attaching formations is not uniform. In the free -swimming larvae the edge hooks, which lie along the edge of the disc with their points facing the ventral side, retain their location, with the exception of the first rwo pairs which unfold and lie with their edges toward the dorsal side. This disposition of edge hooks persists during their entire life among worms of this genus. The large pair of middle hooks, i.e., first from the point of view of time of inception is located on the ventral side but is oriented with its points to- ward the dorsal side, whereas the smaller pair, which is closer to the dorsal side, conversly faces the ventral side with its points. The unpaired middle connecting plate is incepted and lies on the ventral side. The following stage of development of L. elegans (Fig. 186) is characterized p. 169 by the appearance of inceptions of the paired connecting plates. They appear on the dorsal side along the edges of the middle plate and have the shape of straight sticks, sharpened toward the middle line of the disc, and slightly widening toward the opposite end. They are incepted in the interior of the parenchyma of the disc without touching the chitinous elements on either side. During this stage of development the length of worms is about 0. 08 mm whereas the width is about 0. 035 mm; the attaching disc is about 0. 045 mm in width. ftO/wM Fig. 186. Lamellodiscus elegans Bychowsky, young worm from the gills of Sargus annularis from the region of Karadaga (Black Sea). Fig. 187. Lamellodiscus elegans Bychowsky, attaching armature of the disc of developing worms from the gills of Sargus annularis (L,. ) from the region of Karadaga (Black Sea). Explanation in text. 182 At that time the digestive system has grown considerably but the intestine still has a sac -like fornn. At this stage of the division the sizes of the pharynx are about 0.017 - 0.012 mm, i.e., considerably larger than among the free -swimming larvae even though the dimensions of the worm are still approximately equal those of the larva. As was described before, the edge hooks do not grow but remain about 0. 008 - 0.011 mm in length. The middle hooks have the following lengths: the first pair about 0.03 mm, the second 0. 02 mm, the middle connecting plate 0, 012 - 0. 014 mm, and the lateral, paired 0. 008 - 0. 01 mm in length. The further development of the attaching armature proceeds rather intensively. It is characterized by a rapid growth of middle hooks and of the connecting plates which acquire their difinitive shape and sizes (Fig. 187, A) before the beginning of the formation of the attaching plates on the disc. The growth of the middle hooks proceeds as among all pre- ceding species by way of the accretion of the end which is opposite to the point. The connecting plates increase mainly by way of growth on both ends, at the same time they thicken throughout their lengths (Fig. 187, B). The following stage of development is characterized by the formation of both supplementary discs (Fig. 188). They are incepted simultaneously on the dorsal ajid ventral side and at first are hardly p. 170 Fig. 188. Lamellodiscus elegans Bychowsky, young worms from the gills of Sargus annularis from the region of Karadaga (Black Sea); stages of the beginning of development of the supplementary discs. noticeable. However, the inception of these formations takes place in such a way that all their elements are formed at the same time and then gradually grow and thicken. During this stage the digestive system 183 already has its final circular shape, but the sex system has not yet been completely developed. The approximate sizes of the worms during that stage are: length 0. 11 - 0. 13 mm, width 0. 04 - 0. 07 mm; length of the disc 0. 05 - 0. 06 mm with a width of 0. 08 - 0. 09 mm; the pharynx is about 0. 025 x 0. 020 mm; the lengtli 'of the first pair of middle hooks is 0. 043 - 0. 046 mm and of the second pair 0. 038 - 0. 040 mm; that of the middle connecting plate about 0. 045 mm; and of the lateral plates 0. 045 - 0. 047 mm; the sizes of the supplementary discs (at rest) 0. 03 x 0. 035 mm. The further development takes place nnainly by way of the for- mation of the sex system and the strengthening of the structures of the attaching apparatus which serve for the articulation of the middle plates with each other and the middle hooks. Considerable growth of the worms, which increase almost three.^_tj,me s in length in comparison with the stages just described and whixjh already have a fully developed attaching apparatus, takes place during this time. .One must also note that the inception of the copulatory organ takes place almost directly after the formation of the attaching plates and the sex systenn begins to function and the worms deposit eggs much before reaching their final sizes. 11. The development of Calceostomella Palombi P- 171 In contrast to all preceding genera, Calceostomella is characterized by the fact that during the attachment of the adult indi- vidual the basic significance is acquired by the attaching disc itself and not its armature which is developed so weakly that until the present time it was not even really known whether the edge hooks exist, or if they exist what is their number. As our studies of C^ inerme Parona and Perugia have shown, the attaching armature of this species corresponds to that of Dactylogyridae and consists of 12 typical edge hooks and two middle hooks. The adult _C. inermis (Fig. 189) differ by a strongly developed glandular fringe of the anterior end of the body, by relatively large testes and strong development of vitellaria which almost fill the entire body of the animal. The copulatory organ is chitinous, with powerfully developed prostatic glands. The development of representatives of the genus has not been studied. We obtained a free-swimming larva of C. inermis at the Sebastopol Biological Station (on the fifth day after the deposition of eggs); during July, 1935 the worms which were collected from the Gorbil (Corvina nigra Salv. ) (Humpback Salnnon, nobis) in- tensively deposited eggs. The larva which emerged from the egg is cigar- shaped and has a length of about 0. 1 mm and a width of 0. 03 mm. The ciliary epitheliunn is well-developed and of the usual disposition. The eyes number 2 pairs and are relatively large and are located in front of the pharynx. The attaching disc is already sharply separated from the rest of the body in the larvae which emerges from the egg. The interior organization of the larva is the same as in Dactylogyrus . The attaching 184 armature (Fig. 190) is represented by 12 lateral hooks and 2 middle hooks which have the characteristic shape with already developed interior and p. 172 exterior offshoots. The sizes of edge hooks are 0. 012 - 0. 014 mm, the sizes of the middle ones are 0. 010 - 0.011 mm. During subsequent development the nniddle and edge hooks stop growing and among the adult individuals they have the same dimensions. We shall also indicate that during the time of development the growth of the eyes does not take .place and it is possible that among the adults they are reduced (disappear? nobis ) because we were not able to find traces of eyespots among certain adult individuals. O.OInf* Fig. 189. Calceostomella inermae Fig. 190. Calceostomella inermae (Parona and Perugia), young worm from the fins of Corvina nigra Salv. from the Bay of Naples (Mediter- ranean Sea). (Parona and Perugia), attaching armature of a free-swimming larva. 12. The development of Tetraonchus Diesing Among the representatives of the genus Tetraonchus (Fig. 64) the presence of 4 eyes, of a pipe -shaped intestine and of an attaching disc with 16 edge and 14 middle hooks is characteristic; the latter are linked with each other by a single connecting plate. In August of 1949 on the Island of Hanka, A. V. Gussew hatched a considerable number of larvae from the eggs of T. monenteron (Wagener) which parasitize the gills of Esox reicherti Dyb. The develop- ment of larvae within the eggs continued about 3 to 4 days. A number of the hatched larvae were impregnated with silver. We also hatched larvae of T. monenteron (Wagener) from the eggs of worms from Esox lucius L. 185 studied in the Delta of the Volga (June, 1954). The development of the eggs took place approximately with the same speed as on the Island of Hanka and the ennergence of the larvae was observed on the third day. The material obtained was also partially impregnated with silver. Further description is based upon the study of the preparations from both regions. . . viUli,„H//((/,;(,/i ,v,.V J.'. -A: 0.01mm Fig. 191. Tetraonchus monenteron (Wagener), location of ciliary cells of the body of a free-swimming larva. The larva on the left is in dorsal view, and on the right in ventral view. Impregnated with silver. The larvae which emerged from the eggs have the customary elongated form. Their length is about 0. 12 mm with a width of 0. 04 mm; in fixed state they are somewhat shorter--0. 08 - 0. 10 mm long with a width of 0. 06 to 0. 07 nnm. The ciliary covering is located in three zones. In the silvered specimens (Fig. 191) it is evident that each zone consists of a different number of large, rounded cells (with a diameter about 0, 005 mm). The anterior zone lies basically on the dorsal side from the very edge of the body and reaches posteriorly to the level of the first pair of eyespots The edges of the anterior zone extend to the ventral side where they termi- nate, reaching not further than the corresponding eyespot on each side, and in such a fashion the middle of the ventral surface of the anterior edge of the body is deprived of ciliary covering. The total number of cells of the anterior zone equals approximately 32, of which 18 lie on the dorsal side and 6 on each side of the ventral. In opposition to the preceding anterior one the middle zone of ciliary cells lies mainly on the ventral side, only partially extending to the sides of the body. It consists of two sections (about 14-15 cells), which start from the level of the pharynx anc extend posteriorly somewhat further than the edge of the first half of the body of the larva. Both sections of the ciliary cells of the middle zone p. 17: 186 occupy a lateral location, and between them a bare space remains on each side of the body which is considerably larger on the dorsal side and smaller on the ventral side. The posterior zone occupies the entire end of the body and is somewhat more powerfully developed on the dorsal side. The number of cells which compose it is about 17 of which 10 lie on the dorsal side. All in all the ciliary covering of the larva consists of 61 to 62 cells. The attaching disc of the larva is almost not delineated from the body; it bears 16 edge hooks of the typical shape for the genus (Fig, 192), 0, 010 - 0. 012 mm in length. Each hook is equipped with a well- developed little loop and a thin tendon. In addition to the edge hooks, two little parentheses of 0. 007 mm in length, which apparently represent the inceptions of the first pair of nniddle hooks, are visible somewhat closer to the anterior end of the body. These little parentheses are not visible in all preparations and have very indefinite contours, consequently we hesitate to state with conviction that they are nniddle hooks. D.OIhm The inner organization of the larva in preparations has not been sufficiently studied. Strongly developed eye spots are clearly apparent. There are three of them--one pair of the anterior and one large posterior spot fused from two halves, which is equipped with light refracting little lenses on both sides. The anterior eyes have a diameter of about 0. 005 mm whereas the posterior eye is about 0. 01 mm in length and has a width of 0. 03 mm. The light-re- fracting little lenses are about 0. 003— to 0. 004 mm in diameter. The pharynx which lies behind the pos- terior eye is slightly elongated (sagittally, nobis) and is about 0. 015 to 0. 017 by 0. 012 to 0. 014 mm in size. The inception of the intestine is not visible in the larva. Further development is not known. Among the larvae impregnated with silver, attention is drawn by several strongly light-refracting bodies (with a diameter of about 0.001 mm) the edges of which are blackened with silver, these are symmetrically distributed in the body (close to its dorsal side). Their number is very considerable (more than 40) but it is not possible to say what they are without further special study. ,^£i»=> Fig. 192. Tetraonchus monenteron (Wagener), attaching armature of a free -swimming larva. 187 13. The development of Tetraonchoides Bychowsky The curious species, T. paradoxus (Fig. 29) was described by p. 174 us recently from Uranoscopus scaber L. It is characterized by a pipe- shaped intestine and a complex attaching apparatus with four supplementary sucker-shaped growths on the dorsal surface of the attaching disc. The armature of the latter participates in attachment but the main role is played by the powerful attaching disc itself. In 1935 at the Sebastopol Biological Station we obtained free-swimming larvae of this species, but unfortunately the drawings of these larvae were lost. From the notes and indications in our work (Bychowsky, 1937) it is apparent that the larva is devoid of eyes just as are the adult individuals. It has a sac -shaped intestine and only 16 edge hooks on the well-developed attaching disc. Thus the formation of the remaining attaching armature in this species takes place in the postembry- onic period. 14. The development of Nitzschia Baer The representatives of the genus Nitzschia (Fig. 17) have two attaching grooves on the head end and a powerfully developed sucker-shaped disc at the posterior end. The armature of the disc consists of 14 edge and 3 pair of middle hooks; there are no septa on the interior surface of the sucker-shaped disc. The sex system is strongly developed and the testes are very numerous. The sex oriface opens on the ventral side of the body almost along its middle line. They parasitize sturgeons. We studied the development of N. sturionis Abildgaard in July, 1932 during our work on the Caspian Sea (Island of Sara). The larvae were obtained from eggs deposited by individuals collected from the great sturgeon- -Huso huso (L. ). The Nitzschia larva which has just hatched from the eggs has an elongated cylindrical body, but with slightly thickened ends and a slightly inflated middle and three zones of ciliary epithelium (Fig. 193). Its length is about 0. 35 mm and the width is 0. 1 mm. The anterior end of the larva has two clearly expressed thickenings equipped with a number of glands corresponding to the head growths of Dactylogyrus and the attaching organs of the head ends of Epibdella and Benedenia . Directly behind these thickenings are located 2 pairs of large eyes under which, closer to the ventral side of the body, lie 2 large head ganglia of the nervous system. The ciliary covering of the head end of the larva starts from the anterior edge and terminates at a level with the posterior end of the anterior pair of eyes. The pharynx of rounded shape and relatively large dimensions is located somewhat away from the eyes; a small ring-shaped intestine emerges from the pharynx. The second zone of ciliary epithelium starts at the level of the middle of the intestine. It is located nnainly along the sides of the body and terminates near the be- ginning of the attaching disc. The excretory system is easily noticeable; 188 its effering openings, located along the sides of the body, are somewhat dis- placed toward the dorsal side, and are located at the level of the beginning of the second zone of ciliary covering. The structure of the excretory system was not followed through by us but it is completely evident that its longitudinal trunks are doubled on each side. Immediately upon its emergence from the egg, the attaching disc of the larva is well-developed and separated from the body, and all its edges are drawn toward the middle, and at that time it is incapable of functioning. The armature of the attaching disc (Fig. 194) consists of 14 edge hooks and 3 pairs of middle hooks of p. different shapes and sizes just as among adult worms. The attaching disc bears a third zone of ciliary epitheliurn which starts somewhat at the front of the middle of the disc and terminates at its posterior end. The attaching armature deserves special description. The edge hooks have uniformly straight handles and a connparatively power- ful transversal growth of the terminal little hook. Their sizes are more or less the same, their length fluctuates from 0. 019 - 0. 021 mm iust as among adult individuals. The first pair of middle hooks whic . is located near the lower posterior edge of the disc, has the shape of the middle hooks of Dac- tylogyrus which are just completing the 175 01 MM ! '^^^ Fig. 193. Nitzschia sturionis (Abildgaard), free -swimming larva. X 0.01mm ^ Fig. 194. Nitzschia sturionis (Abildgaard), attaching armature of a free -swimming larva. growth of the basal part. Their sizes are about 0. 03 mm. The second pair is located behind the first somewhat away from the center of the attaching disc. In its shape it is an elongated plate with an obliquely- growing upper edge and slightly curved lower edge ending in a somewhat obtuse, rounded "point. " The sizes of the second pair are considerably larger-- 0.048 - 0.050 mm. Finally, the third pair, located almost in the center of the disc of the larva, have the shape of hooks with a slightly widening basal part and with an almost straightened point and lateral off- shoot which lies between the point and the basal part and has a somewhat curved and free end which is directed toward the same side as the point. 189 flfl/«« Generally this hook closely resembles the edge hooks in structure. The sizes of middle hooks of the third pair are about 0. 034 - 0. 036 mna. After a relatively small interval of time after emergence of the larva from the egg, the edge and the middle hooks of the attaching disc "cut through," i.e., their edges protrude outside, while the disc itself unfolds and the larva acquires the ability for attachment. A gradual change of the larva into the adult stage takes place after the attachment to the body of the host and the shedding of the ciliary epithelium. The head thickenings change into the so-called attaching grooves, and the sex t system is developed and the nervous and excretory systems grow and acquire their final form. The pharynx grows quickly and becomes barrel- shaped, whereas the intestine develops and forms a number of lateral branches. Finally, the attaching disc strongly increases in di- mensions and acquires the shape of a powerful sucker. As has already been indicated, the edge hooks do not grow, whereas the middle ones not only grow very intensively but also change their form. The growth of the middle hooks takes place differently (Fig. 195). The first pair grows approximately 4 to 5 times and the growth takes place, as in all middle hooks of the usual type, by way of accretion at the free end of the basal part. The larval hook remains in such a fashion as an unchanged lower part of the hook. The second pair also grows approxi- mately 4 to 5 times, but this growth is different. Here takes place not only accretion at the free end but also a general thickening so that the exterior, lower edge of the hook of the adult individual corresponds to the hook of the larva. Finally, the third pair grows approximately 4 times and growth develops in all directions although in a larger measure in the basal part than near the edge so that although the hook greatly changes in shape it nevertheless remains bifurcated in the lower part just as in the larva. A few words about the biology of the larvae. According to our observations) the attachment of the larvae by their anterior ends to various underwater objects takes place only when the attaching disc functions fully; until that time the larva only feels the encountered obstacles. Fig. 195. Nitzschia sturionis (Abildgaard), attaching armature of an adult worm from the buccal cavity of Huso huso (L. ) near the Island of Sara (Caspian Sea). 176 190 The experiments which we conducted show that immediately upon emerg- ing from the egg, the larva of Nitzschia possess a strong positive photo- taxis and only with the unfolding of the disc does it change into the nega- tive one, in complete conformity with the behavior of the larva of Dactylo- gyrus which was described by us. At the beginning of their lives the larvae swim with unusual speed and force. Upon hatching from the eggs in salt- shakers (stender dishes or test tubes?, at least some type of experimental container, nobis) they immediately "fly out" from them breaking through the film of the surface tension of the water and sliding along the dry surface of the glass for almost a centi- meter above the water. The larvae retain the ability to infest the host fro 5 to 6 hours and after that they lose it although they remain alive and swim in the water approximately 24 hours. 15. The development of Benedenia Diesing The genus Benedenia (Fig. 196) appears to be the typical repre- sentative of Capsalidae. It is characterized by a powerful development of the two head suckers and the attaching disc. The latter is equipped on its inner surface with septa which divide the disc into one central and 7 edge p. 177 sections. The chitinous armature of the disc consists of 14 edge and 6 middle hooks. The internal structure of the representatives of this genus is uniform: There is a well-developed intestine with a large number of exterior and interior branches. The sex system has two large testes and a large ovary and the effering ducts open at the sides of the body. In 1932, Jahn and Kuhn described the development of B. melleni MacCallum, a parasite of American marine fishes, in considerable detail. Then we studied the development of a second species— -B. derzhavini (Layman) from the gill cavity of Sebastodes schlegeli (Hildendorff) in Vladivostok in June, 1949. For the convenience of comparison of the data obtained we shall first give the information concerning the development of B. melleni in the form of a somewhat abbreviated translation from the work of the authors enumerated above and then the data themselves. We must say that we have changed the terminology of Jahn and Kuhn somewhat in line with that accepted by us in the present work. "The free-swimming larva of B. melleni (Fig. 197) is about 0. 23 mm in length and 0. 06 in width, it is flattened at the anterior end and spindle-shaped at the base with the exception of a narrowing in the region of the buccal opening. The posterior one -third of the larva forms an attaching disc which does not function when the larva emerges and which has the sides folded together. The pharynx is rounded, muscular and p. 178 located in the anterior part of the middle third of the body. It opens into a very short esophagus which changes into two relatively large intestinal trxinks which extend almost to the end of the body. There are no lateral outgrowths. 191 There are two pairs of eyes in front of the buccal opening on the dorsal surface of the body. They are in the form of cup-shaped masses of pig- ment, in a cavity of which lie spherical hyaline lenses. The lenses of the posterior pair of eyes are approxi- mately 0.016 mm in di- ameter and lie in front of and to the side of the pig- Fig. 196. Benedenia derzhavini (Lajman), adult worm from the interior surface of the operculum of Sebastodes schlegeli (Hilg. ) near Vladivostok (Sea of Japan) Fig. 197. Benedenia melleni (MacCallum), free -swimming larva. Natural size 0. 23 mm. (According to Jahn and Kuhn, 1932). mented cups. The lenses of the first pair are 0. 012 mm in diameter and lie posteriorly and to the side. The head suckers, which are not fully developed, have the shape of padded sections easily visible in live indi- viduals. The excretory system (Fig. 199) is represented by two relatively large excretory bladders located somewhat behind and laterally to the buccal opening, with 4 canals leading from them, and 10 pairs of flame cells. The excretory system opens in dorsal pairs just as among adult forms. There are 2 large excretory canals each starting from the 1 One must suppose that the description of the authors regarding the number of lateral canals is not accurate because the presence of two basic canals on each side is characteristic for the majority of mono- genetic trematodes in which the excretory systenn has been studied. 192 corresponding bladder and extending posteriorly into the attaching disc. They are connected by a transversal vessel in the posterior part of the body. Each of these canals gives off one branch oriented forward which terminates by one flame cell lying approximately in the middle between the excretory bladder and the transversal vessel. The longitudinal canals extend into the sucker and branch off into five vessels each in the latter. These vessels terminate in flame cells. In addition to the large canals a smaller one leading to the anterior end of the body emerges from each of the excretory bladders. They unite in front of the buccal opening and form ^ the middle canal which leads forward between the . . eyes, beyond which it di- / » • \ vides and branches off to %mt \ ^^® sides. Further, each Fig. 198. Benedenia melleni (MacCallum)^ stages of the development of the larva. Explanation in text. (According to Jahn and Kuhn, 1932). p. 179 Fig. 199. Benedenia melleni (MacCallum), diagram of the excretory system of the free- swimming larva. (Accord- ing to Jahn and Kuhn, 1932). one of the branches bifurcates anteriorly and posteriorly and the branches thus formed terminate in flame cells. There are four more flame cells in the region of the buccal opening lying in front and behind the pharynx. Their canals apparently branch off from the anterlolateral (canal, nobis). Thus, the arrangement of the excretory ducts of the larva amounts to a "circular" system with two lateral pores. The excretory system has a similar structure in adult individuals. The larva is equipped with cilia in the anterior, middle and posterior parts of the body. The anterior ciliary zone extends in front of the first pair of eyes and the cilia practically cover the entire anterior part of the body with the exception of the cephalic attaching organs. The middle ciliary zone starts from the posterior end of the excretory bladders and extends to the posterior end of the body (up to the disc) and covers the sides and the lateral, dorsal and ventral surfaces with cilia. There are no cilia in the middle of the dorsal or in the middle of the ventral surfaces. The posterior ciliary zone occupies the lateral and dorsal surfaces of the 193 posterior two-thirds of the attaching disc. The cilia are relatively long and form from a special epithelium which is clearly visible in live samples. The loss of cilia and ciliary epithelium takes place simultaneously. The attaching disc is folded during the time of the swimming of the larva; it is equipped with middle hooks characteristic for all adult individuals. These hooks lie longitudinally in such a 'vay that their curved ends are located mesially and are visible on the ventral side. The edges of the folded little sucker lie ventrally from the middle hooks and are equipped with lateral hooks. The latter are of equal length, approximately 0.01 mm in length. In live individuals the cephalic attaching organs are very mobile, they even attach themselves to the container in which the larvae are located, and even draw up the entire body behind them. The loss of the ciliary epithelium begins soon after the appearance of this ability. Usually the ciliary covering of the anterior and posterior zones are lost first. The attaching disc unfolds at the same time as the shedding of the epithelium (Fig. 198, A). When it has completely unfolded the middle hooks turn along their long axes and their curved ends protrude outside whereas the lateral hooks are disposed radially along the edge of the attaching disc. At that time the attaching disc already begins to function and attaches to the container. When the larva finds a host, in the beginning it probably attaches by means of the head organs and only afterwards by means of the disc, more precisely by means of its 14 edge hooks and perhaps by means of the posterior pair of the middle ones. After the attachment of the larva (Fig. 198, B) the first noticeable morphological changes are expressed in the transformation of the attaching head organs into the final head suckers. Further, the pharynx which is rounded in the larva acquires the lobed shape very characteristic for the adults. The intestinal trunks begin to put out lateral growths. The diameter of the attaching disc is relatively large in relation to the body. Its middle hooks increase in size and change their form, whereas the lateral do not change and do not grow. Because of this we can deduce that they do not have any significance in the adult form. Further development is expressed mainly in the development of the digestive system and the increase of the excretory system and par- ticularly in the development of the sex system. The size of the eyes in the larva and among the adult is approximately the same. Only their location which is trapezoid-shaped is different among the adults. One must also note that the growth of the (m.iddle hooks of the, nobis) attaching disc proceeds unequally so that at the end of the period of growth the size p. 180 of the middle and anterior pairs is nnore than six times larger than of the sanne ones among young worms, whereas the posterior pair increases only three times" (Jahn and Kuhn, 1932), The free-swimming larvae of^ derzhavini, which have just emerged from the eggs on the 10th day after their deposition are very similar to the larvae of B. melleni, but differ in a number of peculiarities. Their sizes are somewhat larger and the correlation of their parts is different. The length of the larvae is about 0. 26 mm and the width in the middle 194 of the body about 0.07 mm. The body is torpedo-shaped (Fig. 200), rather narrowed at the level of the pharynx and in front of the attaching disc. The latter is well-developed, it is sharply delineated from the rest of the body, and rather larger than among B. melleni. Among free-swimming larvae it is somewhat elongated in length. Its sizes are about 0. 09 - 0. 08 mm. The head end is slightly flattened, the ducts of the head glands open into it by bunches. The latter are rather powerfully developed and lie along the sides of the body between the posterior pair of the eyes and the pharynx. There are no "pad-shaped" sections from which, according to Jahn and Kuhn, suckers are formed. In its structure the anterior end completely corre- sponds to the one among Dactylogyridae, the only difference being that the number of head ducts in B. derzhavini is larger and their size is more considerable. The eyes, which have the usual location, are powerfully developed. The anterior pair is one and one -half times smaller than the posterior in diameter. The lenses of the eyes are large and often of oval form. The digestive system is well-developed. The pharynx is rounded and has a diameter of about 0. 03 mm; from it extends, clearly visible in the live subjects, a sac- shaped intestine which exceeds the diameter of the pharynx by three to four times. In such a fashion the structure of the intestine in our species sharply differs from the one among B. melleni . The excretory system is poorly studied. Two powerful flask-shaped excretory bladders, the dimensions of which exceed the dianaeter of the pharynx, depart from (open outside by, nobis ) the dorsal pores. Two excretory trunks emerge anteriorly and pos- teriorly from the bladders (see note on page 178 ). These canals lie just as they are pictured by Jahn and Kuhn in B. melleni with certain deviations indicated on the drawing. We did not succeed in counting the number of flame cells^ but it is considerable. The ciliary covering of the larva is analogous to the one in B. melleni, but the description of Jahn and Kuhn seems inaccurate to us. The anterior zone lies away from the anterior end of the body at a certain distance and extends posteriorly to the level of the first pair of eyes. It not only leaves the places of the eff erring ducts of the head glands free, but it is also interrupted on the ventral and dorsal sides. The middle zone begins below the excretory bladders and extends up to the disc and apparently forms a break on the ventral side, whereas it extends fully on the dorsal side. The third zone occupies the posterior half of the 0.1 MM Fig. 200. Benedenia derzhavini (Lajman), free -swimming larva. 195 attaching disc but forms a small break on the very posterior end on which a small, hill-shaped growth is located. Altogether the ciliary covering of the larva carries evident traits of bifurcation into right and left independent halves. The casting off of the ciliary epithelium takes place unequally: the p. 181 middle zone is shed last. The attaching armature (Fig. 201) of the larva consists of 14 edge hooks and 3 pairs of middle hooks. The edge hooks are 0. 012 - 0. 015 mm in length. They are of the usual dactylogyrid-form with a handle of constant thickness in its entire length. The sizes of the edge hooks do not change during the entire life of the worms. The first pair of middle hooks lies near d.lMM (LOlMfi Fig. 201. Benedenia derzhavini (Lajman), attaching armature of a free -swimming larva. Fig. 202. Benedenia derzhavini (Lajman), middle hooks of an adult worm from the gill cavity of Sebastodes schlegeli (Hilg. ) near Vladivostok (Sea of Japan). the posterior end of the attaching disc. They have the shape of the middle hooks of Dactylogyridae with undeveloped offshoots resembling the hooks of Nitzschia but relatively more massive. The length of this pair in D. derzhavini is about 0.028 - 0.03 mm. The second pair of middle hooks lie sonnewhat closer to the center of the attaching disc, leaning with the lower half against the first. The hooks of this pair resemble the middle hooks of the lowest groups with a basal part which is long but compressed at the sides and rounded on its free end and changing on the opposing end into a small, sharply-curved point. Along with this, a small sharpened offshoot, as if it were a small second point, departs at the place of its determined beginning along the exterior curvature of the hook in the opposite direction. The length of the hook of the third pair is about 0. 038 0. 04 nnm. The third pair of middle hooks lies almost at the center of the attaching disc and has the shape of little sticks bifurcated at the lower end 196 and rounded at the upper end. The hooks of this pair are very similar to the corresponding ones in Nitzschia. Their sizes are 0. 026 - 0. 028 mm. In their description of the development of B. melleni, Jahn and Kuhn do not indicate that the growth of the middle hooks is accompanied by changes in their shapes. In B. derzhavini they are considerable which is apparent from the comparison of the nniddle hooks of the larvae with those of the adult animals (Fig. 201 and 202). The growth of the separate pairs of the middle hooks is also unequal in B. derzhavini; thus the first pair increases in length about 6 times^ whereas the second about five times and the third 9 times. Thus the tempo of growth and its correlation among middle hooks of both types of Benedenia which were studied is completely different. The development of the larvae until the adult stage is analogous to the one which we saw in Nitzschia sturionis Abildgaard and Benedenia melleni (MacCallum) p. 182 16. The development of Polystoma Zeder We have at our disposal materials on the development of three species: P. integerrimum Froelich, P. nearcticum (Paul), P. ozaki Price. A number of authors studied P. integerrimum (Zeller, 1872a, 1876; Halkin, 1901; Goldschmidt, 19"02a, 1902b; GaTlien 1932a, 1933, 1934b, 1935). It was studied with a considerable degree of completeness starting from cleavage. From the fall of 1927 until the fall of 1929 we also conducted research on the development and life cycle of P. integerrimum, which unfortunately remains unpublished. We shall note that P. integerrimum is characterized in the adult stage by the presence of 6 suckers on the attaching disc which also serve for the attachment of the animal. The chitinous armature of the disc, which exists among adult worms, either does not play any role at all in attachment (edge hooks) or an extremely insignificant role (middle hooks). As is known, there are two mature forms in the life cycle of P. integerrimum : one which grows slowly and parasitizes Fig. 203. Polystoma integerrimum the urinary bladders of frogs, while Froelich, free -swimming larva. the other, with a quick tempo of Natural size about 0. 3 mm. (Accord- development lives in the gill cavity ing to Halkin, 1902). of the tadpoles. Taking into con- sideration that both of these forms, have, in addition, a different morphology (Figs. 22, 127) one could expect 197 the presence of tAvo different types of larvae which would develop from eggs deposited by these different forms. However, actually the free- swinnnraing larvae which have just emerged from the eggs of gill Polystoma do not differ morphologically from those from the eggs of polystomes which parasitize the urinary bladder. The eggs of P. integerrimum are deposited in the water and the cleavage takes place already in the external medium, among the individuals from the urinary bladder just as among forms from the gill cavity. The free-swimming larva of P. integerrimum Fig. Z04. Polystoma integerrimum Froelich, the location of the ciliary cells on the body of a free-swinnming larva. Left in ventral and right in dorsal view. Impregnation with silver. Schematically. is more complexly organized than all the preceding forms, mainly by way of the increase of the ciliary covering and its greater differentiation, and of the separate parts of the body. The larva (Fig. 203) has an elongated body shape which slightly narrows toward the anterior end, and also has a well-expressed attaching disc. The latter is folded in the beginning and then unfolds after a very short period following the emergence of the larva from the egg. The sizes of the larvae are relatively large: the length is about 0. 3 mm and the width is about 0. 07 - 0. 09 mm. The ciliary covering is distributed in three zones (Fig. 204) just as among the previous types; however, these zones have a more complex structure and lie not only along the sides of the body but extend also to the dorsal and ventral surfaces. For the study of details of the location of the ciliary- covering of P. integerrimum we, together with T. Tsiborskayia, a colleague of our laboratory, conducted a special research in which we utilized the method of silvering widely accepted for the study of the p. 183 198 simplest forms and which has already been applied to Monogenoidea (see page 187 ). First of all, our data affirmed that the number of cells of ciliary epitheliuna annong larvae of Polystomatidae is constant as was supposed earlier and first determined by Ozaki (Ozaki, 1935b). Altogether the ciliary epithelium of the larvae of P. integerrimum consists of 55 cells. It is characteristic that the cells of the ciliary epithelium do not form a continual covering but each of them lies separately (lie in separate zones, nobis). The first zone of ciliary cells is located in front of the first pair of eyes and consists of 25 cells located (symmetrically in relation to the mesial line of the body) in two groups. The first group consists only of one cell which lies terminally or more often is slightly displaced to the dorsal side; the 18 cells of the second group are located on the ventral side as a belt completely encompassing that side of the body of the larva, whereas the remaining 6 cells of this group are located on the dorsal side with three on each side so that the basic part of the dorsal surface is deprived of ciliary epithelium. The second zone consists of 18 ciliary cells divided into two groups, of which the first lies approximately at the level of the middle of the pharynx and the second somewhat toward the front of the anterior end of the attaching disc. The first group has 6 cells p. 184 located on the dorsal side, three on each side of the body so that the edge cells are easily visible from the ventral side of the larva. The first group of this zone consists of 12 cells lying symmetrically in a group of 6 cells on the ventral and dorsal sides. Finally, in the third zone, 12 cells lie on the dorsal side of the posterior half of the attaching disc somewhat away from its posterior end so that the 2 edge ones on each side are clearly visible from the ventral side when the larva is observed. In such a fashion 24 ciliary cells are located on the ventral side of the larva, while on the dorsal--30, and finally one cell lies terminally. Apparently such an unequal distribution of cells appears to be the reason for the peculiar swaying motion of the free -swimming larva. The head end of the larva is equipped with four groups of glands. Four pigmented eyes of the larva with well-expressed lenses are located somewhat in front of the pharynx. The digestive system is rather powerfully developed. The pharynx is somewhat extended in length (0. 04 x 0. 03D mm), it lies at the end of the first and the beginning of the second third of the body. The intestinal tract emerges from it in the form of a small esophagus. The intestinal tract is elongated, with 2 branches which merge in the end of the body. Between the 2 branches of the intestine there is one, or more rarely, 2 anastomoses lying approxi- mately in the middle part of the intestinal space. The excretory system is well-developed. Its openings are located along the sides of the body and on the dorsal side and somewhat behind the pharynx. There are also small excretory bladders. The trunks of the excretory system, which lead to the posterior and anterior ends of the body on each side, apparently do not form transversal connecting canals. One must note that we our- selves did not study the excretory system, and all the existing descriptions 199 and drawings of it among P. integer rimum are too schematic. The at- taching armature of the disc of the larva is represented by 16 edge hooks and a pair of middle hooks (Fig. 205). The edge hooks are of the typical shape with a well-expressed transversal growth between the terminal hooks and the handle. The middle hooks have the shape of small chitinous little parentheses of smaller sizes than the lateral hooks. The length of the edge hooks is 0. 028 - 0. 032 mm and of the middle hooks 0. 018 - 0. 02 mm. After its attachment to the gills of the host and loss of the ciliary epithelium the fate of the larva is twofold. In the case of accelerated growth, the formation of the gill form (see page 121 and Fig. 127), its metamorphosis is Fig. 205. Polystoma integerrimum acconnpanied by intensified feeding, Froelich, attaching disc of a free- in connection with which the intestine swimming larva. Strongly com- grows considerably. The latter pressed. acquires sac-like form with vague outgrowths along the exterior edge and a few interior anastomoses. The posterior end of the intestine extends into the attaching disc cind even occupies a large part of it. The sex system of the type different than the one which parasitizes the urinary bladder develops quickly. Its basic peculiarities are: a strongly elongated and p. 185 sausage -shaped ovary; the absence of vaginal ducts and of the ductus g enito - inte s tinali s ; the absence of the uterus proper and the presence only oi the ootype in which the eggs are formed one at a time; and finally the presence of one testis of a rounded form. The attaching disc grows un- equally. The lateral hooks remain without change in shape and size, whereas the middle hooks grow relatively little reaching 0. 04 - 0. 045 mm in length, and do not form any offshoots. Subsequently starting from the posterior end of the disc, suckers are incepted at the places of 3 pairs of lateral hooks (6th, 5th, and 4th) in such a fashion that the lateral hooks eventually are located in the centers of the sucker. For the most part, the sizes of the suckers remain unequal during the entire life of the worm, the posterior are larger and the anterior are smaller. The attaching disc is often strongly deformed and has an irregular shape, depending to a great degree on the size and nature of the gill cavity of the host. Among the larvae which develop into the adult form in the urinary bladder the development takes place much slower and the worms reach their final structure only in the second year of their life in contrast to the gill forms all the development of which takes place within a few weeks. The larva begins its metamorphosis on the gills of the tadpoles succeeding largely in forming the first and second pair of suckers. It is true that these suckers do not as yet have the final form and dimensions (Fig. 206, A and B). At the sanne time with the metamorphosis of the tadpoles and the loss of the 200 gills by them, the larva of ^ integerrimum passes through the intestinal tract to the urinary bladder where it finally settles. The last pair of the suckers of the larva Fig. 206, C) develop in the urinary bladder and it terminates its metamorphosis. The growth of the individual continues during its entire life, i. e. , about 4 to 5 years, whereas maturity is reached at the end of the second year. The attaching disc of Polystoma of the urinary bladder is >srell-expres8ed and delineated from the rest of Fig. 206. the larva. Polystoma integerrimum Froelich, stages of metamorphosis of Explanation in text. (According to Zeller, 1872). the body from the very beginning of its development. Just as among the gill form, the edge hooks do not grow, whereas the middle hooks reach considerable sizes -forming both offshoots and apparently grow during the greater part of the life of the individual (at any rate after it reaches ma- turity). Suckers are formed around the same pairs of lateral hooks but have a more regular shape and already at the end of the first year they have the same sizes while continuing, at the same time, to grow for a relatively long time. The intestinal tract acquires its final shape, with three characteristic internal anastomoses by the end of the first year ot life. The sex system differs from the one of the gill individuals by a more compact structure of the ovary and the presence of the ductus genito-intestinalis, 2 vaginal ducts, an elongated uterus capable of holding more than two dozen eggs, and with a large follicular testis. It is interesting that the structure of the copulatory organ in both forms is identical; also identical in form and number are the hooks which are located as a wreath at the base of the penis. p. 186 The development of P. nearcticum (Paul) was studied by the author of the species (Paul, 1938) and it is very similar to the one of P. integerrimum. It is interesting that the gill form is also discovered in this 201 species which means that this is not an exclusive peculiarity of P. integerrimum but is common to the entire genus or at any rate to a number of its representatives. P. ozaki Price apparently has a similar development to P. integerrimum but with a more delayed tempo. This type resennbles the first extremely closely but differs by 0.07MH Fig. 207. Polystomoides oris Paul, free-swimming larva. (According to Paul, 1938). 1\m Fig. 208. Poly stomoide s oris, Paul, two stages of developmient of the young worms from the buccal cavity of the turtle Chrysemys picta (Schneider). (According to Paul, 1938). a powerful development of the digestive system. We have observed the process of nnetamorphosis of the larva of this species in the young frog (Rana chensinensis Dov. ) on southern Sakhalin in the regions of Antonov in 1946~ The larvae -reached the urinary bladder of the frog at earlier stages than among P. integerrimum , i. e. , while they do not even have the first pair of suckers. 17. The development of Polystomoides Ward The genus Polystomoides is characterized by the presence of one large testis, by the absence of a uterus (there is only an ootype), and by simple, unbranched intestinal trunks (Fig. 82). Paul (Paul, 1938) worked on the development of P. oris Paul fronn the buccal cavity of Chrysemys picta (Schneider). The larva develops in the eggs for approxi- m.ately 28 days. Upon emergence from the egg it swims freely, thanks to the four zones of ciliary epithelium (Fig. 207). The structure of the larva is very simdlar to that of the representatives of the genus Polystoma . Its sizes are 0. 275 by 0. 065 mm. The attaching disc bears 16 pairs of p. 187 202 edge hooks and 2 pairs of middle hooks of which one pair is larger. The sizes of edge hooks do not change in the process of further development of the larva and remain about 0. 03 mm during the entire life. The smallest pair of middle hooks in the larva is 0. 035 mm and grows among adult worms up to 0. 065 mm. Finally, the larger pair changes its sizes from 0. 035 to 0. 12 mm. The fate of the larva which reaches the buccal cavity of its host where the adult worms live is poorly studied; however, in general traits its development apparently is analogous to that of Poly- stoma (Fig. 208). 18. The development of Diplorchis Ozaki The genus Diplorchis is also close to that of Polystoma but differs by simple unbranched intestinal trunks, the presence of 2 testes, and by the very powerful development of the uterus which extends pos- teriorly to the attaching disc, filling the middle part of the body of the worm almost fully, and almost completely displacing the parenchyma and the vitellaria beyond the intestinal trunks. Ozaki (Ozaki, 1935b) worked on the development of D. ranae Ozaki. He observed the deposition of eggs and also gave a good description of the free-swimming larva. The eggs of D. ranae begin to develop in the uterus of the parent individual. The eggs which are deposited contain fully formed larvae (Fig. 209). The free-swimming larva which emerges from the egg which is already in the water has a cigar-shaped, elongated form (Fig. 210). Its length is 0. 24 - 0. 28 mm and its maximum width is about 0. 08-0.1 mm. Its widest part is between the anterior end and the pharynx; its anterior end is rounded, the attaching disc is well-delineated. The ciliary covering of the larva of D. ranae (Fig. 211) was studied by Ozaki by means of the silver impregnation technique. Thus, the precise distribution and numbers of ciliary cells was clarified. Their total number is 59. The cells are distributed in 5 groups lying symmetrically on the ventral and dorsal surfaces and extending to the lateral edges. The first group consists of one cell on the anterior, terminal end of the body of the larva. The second consists of 26 cells located in a continuous mass on the ventral surface of the larva fronn the buccal opening posterior to the first half of the pharynx. The third group is located at the level of the posterior edge of the pharynx and extends somewhat behind. It consists of 3 pairs of cells along the sides of the body of the larva. The fourth group is located near the posterior end of the body and consists of 12 cells forming a little belt along the dorsal side and the edges of the body and extending only slightly onto the ventral surface. Finally the fifth group consisting of 14 cells is located on the sides and the dorsal surface of the posterior half of the attaching disc. Comparing the ciliary covering of D. ranae with that of Polystoma integerrimum we see an almost 203 p. 188| Fig. 209. Diplorchis ranae Ozaki, ripe eggs with formed larvae. (According to Ozaki, 1935). Fig. 210. Diplorchis ranae Ozaki, free-swimming larva. (According to Ozaki, 1935). Fig. 211. Diplorchis ranae Ozaki, location of ciliary cells on the body of free -swimming larva. A--In ventral view; B--In dorsal view; C--In lateral view. (According to Ozaki, 1935). 204 complete resemblance although the number of cells in P, integerrimum is somewhat smaller and their location is such that we prefer to speak of three and not five zones of ciliary epithelium. There is no doubt that the 5 zones of cells in D. ranae represents the next step in the differentiation of the ciliary epithelium. This is seen especially clearly in the examination of D. ranae from the dorsal surface (Fig. 211). For we can observe from that view the rapprochement between the first and second, third and fourth groups of ciliary cells, i.e. , their three-zoned distribution. There are 2 pairs of pigmented eyes located at the end of the first third of the body. The digestive system is represented by the barrel-shaped pharynx located posteriorly to the eyes, by a short esophagus and two intestinal trunks which end blindly without extending into the attaching disc. The excretory system (Fig. 212) of D. ranae was studied by Ozaki fairly accurately. It is of the same type as among Polystoma. It is well-developed. The excretory openings lie dorsally along tl^ sides of the body at the 189 Fig. 212. Diplorchis ranae Ozaki, excretory system of a free- swimming larva. (According to Ozaki, 1935). Fig. 213. Diplorchis ranae Ozaki, attaching armature of the disc of the free -swimming larva. (According to Ozaki, 1935). level of the esophagus. The attaching armature (Fig. 213) is represented by 16 lateral hooks lying along the edge of the disc and by 2 middle hooks. The lateral hooks are of the same type as among Polystoma , but are of two sizes. The first 7 pairs are small, 0. 017 - 0. 02 mm in length and the 8th pair is almost twice as large — 0. 034 - 0. 038 mm. The middle hooks have the shape of straight needles, slightly thickened near the lower terminal; their length is 0. 022 - 0. 027 mm. Further development of D. ranae has not been studied but apparently proceeds as among Polystoma . The presence of a gill form is unknown. 205 In 1941 Rogers (Rogers) described a new species of Diplorchis (D. scaphiopi) from the f rog, Scaphiopus bombifrons Cope (United States of America, Oklahoma), and gave a short description and schematic repre- sentation of the free -swimming larva of that species. Judging from the data of Rogers the larva of D. scaphiopi hardly differs from the larva of D. ranae Ozaki. 19. The development of Neopolystoma Price p. 190 In the summer of 1949, U. A. Strelkov, a collaborator of our laboratory, studied N. palpebrae, a parasite of the far-eastern turtle Amyda sinensis (Wieg.), which he described in 1950 (Fig. 50). This species appears to be a typical representative of the genus; the latter was charac- terized by Price (Price, 1939) as being very close to Polystomoides and Polystomoidella but differs from them in the absence of middle hooks. Development in the eggs of N. pal- pebrae takes place in Z4 days. The I A -K \^ /"^i.^ ( -\ •»-=c^ \K C=5=^ Fig. Z14. Neopolystoma palpebrae Strelkov, the larva of which emerge from the egg (ciliary covering?), strongly compressed. Fig. 215. Neopolystoma palpebrae Strelkov, attaching armature of the larva which has just emerged from the egg. larva which emerges from the egg (Fig. 214) is apparently covered with a continuous very small and tender ciliary covering. U. A. Strelkov and A. V. Gussew, who together observed the free-swimming larvae, in- dicated that the ciliary covering of N. palpebrae is scarcely noticeable; in the beginning it even seemed to thenn that the larvae were completely devoid of ciliary coverings. The larva has the usual shape for the Poly - stomatidae; its length is about 0. 3 mm and its width is about 0. 1 mm. The attaching disc is rounded, sharply delineated from the rest of the body and has a diameter of about 0. 08 mm. The larva has four eyes located in the customary places, the digestive system consists of a 206 rounded pharynx about 0. 03 mm in diameter and two intestinal trunks which end blindly. The esophagus is practically absent or very short. The excretory system was not observed. The attaching armature of the disc (Fig. 215) consists of 16 edge hooks of the usual form for Poly- stomatidae and of the same length--0. 015 mm. According to the observations of U. A. Strelkov and A. V. Gussew the free-swimnning larva moves relatively slowly and begins to stop rather quickly and to "feel" the bottona of the container. The method of infection of turtles and the further development of N. palpebrae are not known. 20. The development of Sphyranura Wright The structure of the trematodes of the genus Sphyranura, which parasitize the gills of Necturus, is very odd. In addition to the peculiarities of the structure of the sex and digestive systems, adult worms of this genus (Fig. 35) are characterized mainly by the structure of the attaching apparatus. The latter is represented by a well-developed disc bearing 2 powerful suckers, 16 edge hooks, of which two lie in the center of the suckers, and 2 large middle hooks (Fig. 216). p. 191 p. 192 In 1936 Alvey studied the development of Sph. oligorchis Alvey, although in our opinion not thoroughly enough. The development of eggs took place in the external medium during a prolonged period of time. Alvey removed the developing larvae from the eggs from the 26th day of development and then obtained free-swimming larvae emerging 01 MM Fig. 216. Sphyranura osleri Wright, attaching disc of an adult worm from the gills of Necturus sp. from the Huron River (Michigan, U.S.A. ) from the egg on the 27th to the 29th days (Figs. 217 - 218) and finally studied them after attachment. The indications of the author that the larvae are almost completely deprived of ciliary covering are very strange because according to his own observations they are very mobile and swim with the help of their disc (? !). We think that actually the 207 larvae of Sph. oligorchis has a ciliary covering of the same type as Neopolystoma palpebrae which the author was unable to find. The larvae ennerge from the egg with a greater or lesser development of the attach- ing armature and of its separate parts (Fig. 219), but they already have the Fig. 217. Sphyranura oligorchis Alvey, larva which emerge from the egg on the 27th day of develop- ment. Magnified 188 times. (According to Alvey, 1936). Fig. 218, Sphyranura oligorchis . the subsequent stage of develop- ment of the larva. Magnified 215 times. (According to Alvey, 1936). same relations of the disc and armature as the grown forms , i. e. , edge hooks of the final size, 2 middle hooks and 2 suckers. The middle hooks and both suckers do not have the final form or dimensions and grow for a long period of time. The sizes of the edge hooks of the larva are about 0. 25 mm, the length of the middle hooks is about 0. Oil mm^. The internal organization of the larva was poorly studied by the 1 Alvey erroneously wrote 0. 25 and 0. II mm; we verified this from his figures. author. It is known that there is a more or less well-developed pharynx and a small circular intestine. The eyes are absent just as among adult worms. The excretory bladders lie along the sides of the intestine and are easily noticeable in the larva. The development of the sex system takes place, according to Alvey, in about 2 months. 208 21. The development of Diclybothrium Leuckart The genus Diclybothrium is characterized by the presence of the attaching disc with 3 pairs of clamps or suckers, in each of which lies one large chitinous hook. On the posterior end of the disc there is a strongly developed, narrowed part which bears 3 pairs of large hooks (of which two are almost the same size as the hooks of the attaching clamps), one pair of very small hooks and one rudimentary pair of suckers. The typical representative of the genus, D. armatum Leuckart, (Fig. 51), parasitizes the sturgeon family. The study of the develop- ment of this species was conducted by us together with A. V. Gussew (Bychowsky and Gussew, 1950). We cite a section of this work relative to the development of D. armatum below. Fig. 219. Sphyranura oligorchis. stages of development of middle hooks. A- -On 26th day of develop- ment; B--Of the larva which has just emerged from the egg; C-- Of an adult worm. Magnified 130 times. (According to Alvey, 1936). "Attempts to obtain free- swimming larvae of D. armatum were made by us in 1931-1932 but were unsuccessful in the fresh-water region (Delta of the Volga) as in the sea (Island of Sara, Caspian Sea). Only in 1947, during our studies at the VNIRO fish production station in Saratov did we succeed in obtaining two free -swimming larvae from a considerable number of eggs which p. 193 were isolated for development and which, in the main,perished in the early stages of development. A rather large number of the developed larvae could not emerge from the eggs because a rich vegito-bacterial fauna developed on the surface of the latter which prevented the larvae from opening the operculum of the egg. The embryology of the larvae took place in large salt-shakers (stender dishes or embryo dishes? nobis) which were located in a shady place. Temper- atures fluctuated strongly during the entire period of development and within a 24-hour period. The tennperature during the entire period of the development of the larvae fluctuated from +20, to +30. 0° centigrade and within the limits of 24 hours the difference was up to 6°. In spite of these clearly unnatural temperature conditions, development took place rather quickly, in comparison with that of other large monogenetic trematodes. On the 6th day lively larvae were already formed in the eggs, and on the 8th day they emerged. Taking into consideration the abnormal conditions of the experiment one must suppose that in nature the development of D. 209 armatum takeB place in approximately 2 weeks. The larva, which has just emerged from theegg ,is torpedo-shaped and is about 0. 4 mm in length when the width of the body is about 0. 18 mm. The attaching disc is clearly delineated from the rest of the body and has a length of 0. 08 mm and a width of about 0. 16 mm. There is a ciliary epithelium dis- tributed in three zones on the surface of the body of the larva. The first zone occupies the surface of the anterior end of the body, extends posteriorly to the level of the pharynx and consists of two sections of ciliary epithelium lying along the edges of the cephalic end and ex- tending sonnewhat onto the dorsal and ventral surfaces of the body. Both of these sections begin some- what away from the anterior end so that the extreme anterior end is free of cilia. The second zone be- gins somewhat above the middle, extends posteriorly almost to the beginning of the attaching disc and is located also in two sections along the sides of the body and also extending somewhat onto the dorsal and ventral surfaces. The third zone is located on the attaching disc, and consists of two lateral sections which begin on the anterior edge of the disc and terminate somewhat just short of its posterior end. Fig. 220. Diclybothrium arnnatum Leuckart, free-swinnming larva. (According to Bychowsky and Gussew, 1950). The anterior end of the body bears 2 pairs of rather well- developed eyes located in front of the pharynx. The posterior pair is somewhat larger than the anterior. The pharynx is more or less rounded, about 0. 04 mm in diameter. From it extends the circular intestine of somewhat elongated shape which reaches posteriorly almost to the anterior edge of the attaching disc. The excretory system was not discovered during the studies of both samples. The attaching disc bears a powerful and complex armature consisting of 7 pairs of chitinous hooks of three different types (Fig. 221--B.B.). Among them five pairs are of the same shape and size and are located along the edge of the disc and two pairs differing (from each other, nobis) in shape and sizes and sharply differing from the edge ones lie in the nniddle section of the disc. The lateral hooks resemble those of the dactylogyrid-type; they have a strongly developed hooked part proper and a rather thin, long handle. The in- terior offshoot of the hooked part is widened in the middle and its sharpened free end is oriented toward the same side as the handle. The sharp points of the lateral hooks are rather strongly curved. Each lateral hook is equipped with a chitinous loop of rather large size customary for all highest monogenetic trematodes. The 1st pair of 210 middle hooks is much more massive than the lateral ones with a widened and bifurcated upper part. The exterior offshoot of these hooks is some- what sheered (truncated, nobis) at its free end-, whereas its interior is more rounded and massive. The 2nd part of the middle hooks is con- siderably longer than the first and has a strong point which then sharply curves into a slightly curved handle which has almost a uniform width along its entire length. The length of the lateral hooks is about 0. 02 mm and the length of the 1st pair of the middle hooks is about 0. 027 - 0. 029 mm and that of the second- -0. 045 - 0. 055 mm. OMfMM Fig. 221. Diclybothrium armatum Leuckart, attaching armature of the free -sw^i naming larva. "There is no doubt of the homology of the chitinous hooks of the larva with those of the adult animals. The anterior 3 pairs of lateral hooks correspond to the hooks of the suckers --clamps, the 4th pair to the 3rd pair of hooks of the narrowed part of the disc, the 5th pair corresponds to the small hooks of the posterior end and in such a fashion is the only one of them all not subjected to any noticeable change in sizes or form. The Ist and 2nd pairs of the middle hooks of the larva correspond to those of the narrowed part of the disc of the adult individual. It is curious to note that the lateral hooks, strongly differing in form, and the 2nd pair of middle hooks of the larvae acquire a very considerable sinailiarity during further development. It is essential to bear this circumstance in mind during the evaluation of the interrelations of the chitinous formations of adult individuals for the formulation of phylogenetic links within the limits of the group. " 211 22. The development of Mazocraes Hermann Just as all of the subsequent genera, the genus Mazocraes is characterized by the presence of special clamps on the attaching disc which serve for the attachnnent of the animals. As has been indicated, these clamps have a connplex structure because of the presence of a large number of chitinous parts of systematic significance. The genus Mazocraes (Fig. 24) is directly diagnosed as Mazocraeidae which have 4 pairs of clamps, 2 large middle hooks and 2 pairs of smaller hooks of different sizes on the attaching disc. The basic difference of this genus from the one closest to it is the special structure of the chitinous parts of the male copu- latory organ. During our work on the Caspian (Island of Sara, 1932 and 1955) and Black (Sebastapol, 1955) Seas we often obtained early stages of the development of M. alosae Hermann- -typical parasite of herring -type fishes. The free- swimming larvae emerge from the eggs on the fourth to the sixth day They are strongly elongated in length, cigar -shaped with a weakly delineated attaching disc. Their length is about 0, 2 mm their width is about 0. 08 mm. The ciliary covering is distributed along the sides of the body extending onto the dorsal eind ventral surfaces. It Mazocraes alosae Hermann extends from within a short distance of the anterior end of the body to the anterior edge of the attaching disc and then is located on a cone-shaped growth beyond the disc. The lateral p. 195 01 KM Fig. 222. free -swimming larva in ventral (on the left) and dorsal (on the right) views. zones of the ciliary epithelium are divided into five cells on each side of the body. Between the cells there are some small but clearly visible sections which are free of ciliary epithelium. The posterior zone is divided into two groups between which lies a relatively large section which forms the rovmded apex of the posterior cone which is free of cilia. The anterior end of the larva is slightly rounded and behind it is located a glandular depression slightly divided into two halves. On each side of it (the depression, nobis) and somewhat behind are two pairs of offering ducts of the head glands. Approximately between the first and second 212 quarters of the length of the body a pigmented eye is located lying mesially from the ventral side of the body. This eye has the shape of a slightly elongated rectangle and apparently is fused from two; the sizes are about 0. 001 X 0. 005 mm. The eye, well-developed in the larva, disappears rather quickly after the attachment of the latter. The digestive system is represented by a strongly developed pharynx and a sac -like intestine. The pharynx is rounded and is about 0. 03 mm in diameter. The intestine, which occupies approximately the third quarter of the length of the body, has a narrowing in the middle part and a small invagination in the middle of the posterior edge forming, in this fashion, 2 posterior lobes. During further development these lobes give rise to two intestinal branches. The attaching disc of the larva is equipped with a pair of larger (middle) hooks and 5 pairs of edge hooks (Fig. 223). The large hooks are rather massive with a hard, straight handle and rather powerful point. Their sizes are about 0. 028 to about 0. 03 mm. The edge hooks have a tender, flexible handle and their terminal little hook is of a different form than among all the preceding species: it is more elongated with a straight edge. The sizes of edge hooks are about 0. 2 mnn. During further development the chitinous hooks of the larva suffer different fates. The large hooks which lie at the very posterior end of the disc and one pair of edge hooks which is located side by side with them are preserved during the entire life of the animal without any change in shape and sizes. The fate of the second to fifth pairs of edge hooks is completely different. Very soon after the attachment of the larva, the 1st pair of attaching clamps begins to form on the place and foundation of the 2nd pair of edge hooks and then subsequently in the place of the 3rd pair of hooks --the 2nd pair of clamps, etc. until all 4 pairs of clamps charac- teristic for the adult forms are finally formed. Simultaneously with the beginning of the formation of the 1st pair of clamps on the attaching disc a pair of large middle hooks which have a final form similar to the one in Dactylogyrus, with very powerful exterior and somewhat weaker interior offshoots, is incepted and begins to form. Thus the adult form retains 2 pairs of hooks of the larva without any changes and acquires one pair dur- ing the postembryonic development. The tempo of development of attaching clannps was not followed through by us; however, we must note their characteristic peculiarity, i, e. , their ability to grow. One can Fig. 223. Mazocraes alosae Hermann, attaching armature of the free- swimming larva. p. 196 213 easily see that the younger pairs have considerably smaller sizes on an individual in the process of development which as yet does not have a full number of clamps. The inception of each pair takes place simultaneously, although in rare cases we happened to observe the inception of one clamp somewhat earlier than the other (clamp of the same pair, nobis). 23. The development of Octostoma Kuhn (= Kuhnia Sproston) During our work in southern Sakhalin in August-September, 1946, we obtained the free-swimming larvae of ^. scombri Kuhn. Approximately at the same time, the larvae of this species were obtained from European herring by Gallien and Calvez (Gallien and Calvez, 1947),. Adult forms of Octostoma (Fig. 25) are similar in the structure of the p. 197 Fig. 224. Octostoma scombri Kuhn, free -swimming larva. attaching apparatus to Mazocraes, differing by a somewhat large develop- ment of their chitinous parts. According to our data the free-swimming larva (Fig. 224) is spindle-shaped with rounded ends and the greatest width is in the middle of the body. The length of the body of the larva is about 0. 23 to 0. 26 mm when the width is 0. 08 - 0. 1 mm. At first the attaching disc is delineated from the body rather weakly but soon unfolds and then extends laterally beyond the general contour of the body. Behind 214 the attaching disc there is a large pyramidal growth which is shed at the same time as the shedding of the ciliary epithelium. The ciliary covering is distributed along the sides of the body extending somewhat to the dorsal and ventral surfaces. The cells of the ciliary epithelium lie in a con- tinuous layer from the anterior to the posterior end including the pyra- midal growth. Epithelial cells are flat, elongated and lie with their posterior edges leaning slightly against the following cells. Often one or two of the epithelial cells falls off considerably later than the others and then their borders are even more visible. The anterior end of the larva is equipped with cephalic glands. A large pigmented eye is located be- tween the first and second fourths of the body. This eye does not have P- 1^8 regular contours and varies from a pyramidal to a tetrahedral shape. Often the pigmented granules of the eye scatter around, so to speak, and the eye gives the inripression of degenerating in the larva which has just emerged from the egg. Below the eye is located a rounded pharynx, be- yond which lies the metabolizing sac -shaped intestine of irregular shape having microgranular contents of greenish color. The attaching disc bears exactly the same armature (Fig. Z25) as among the larvae of -„, -,jA .)^ Mazocraes alosae Hermann. The sizes of the 5 pairs of edge hooks "''''^^^ ^^^ ^ P=^ fluctuate around 0. 02 mm and of the larger pair--about 0.022 mm. The gradual loss of the ciliary Fig. 225. Octostoma scombri Kuhn, epithelium begins after the attach- attaching armature of the free- ment of the larva. It starts from swimming larva. the middle of the body and continues progressively to both ends. The posterior pyramidal growth falls off last; at that time the edge hooks unfold and cut through. Further development proceeds just as among Mazocraes alosae. We shall note that the middle hooks which are in- cepted later reach considerable sizes among adult individuals, and take an active part in attachment. The data of Gallien and Calvez basically coincide with ours; however, the only difference is that they did not notice the differences in sizes of the chitinous hooks which, it is true, are very insignificant. 24. The development of Diclidophora Diesing ( = Dactycotyle Beneden and Hesse, Dactylocotyle Marshall) The genus Diclidophora (Fig. 54) represents a large group of marine monogenetic trematodes which are characterized by the presence of 8 sucker-shaped clamps on the disc and by a system of chitinous plates 215 which, in contrast to the plates of Mazocraeidae, are strongly dismembered and serve nnainly as the supporting apparatus of the suckers. The three species of this genus for which larvae are known are: D. luscae (Beneden and Hesse), D. poUachii (Beneden and Hesse), and D. denticulata (Olsson). The larvae of the first two species were studied by Gallien (Gailien, 1934a), but it is we who obtained the last one from the eggs which were brought to us alive by A. V. Gussew and U. I. Polianski from the Norwegian Sea. The eggs of D. denticulata were gathered by them from parasites from the gills of the Pollack- -Pollachius virens (L. ). Upon ennergence from the eggs the larva of Diclidophora (Fig. 226) swim freely with the help of the ciliary epithelium which is located just as it is among the Mazocraes with a break at the level of £.1mm 001mm Fig. 226. Diclidophora denticulata (Olsson), free-swimming larva. Fig. 227. Diclidophora denticulata (Olsson), attaching armature of the free -swimming larva. attaching disc. The dorsoventrally flattened larvae are transparent. The length of the larvae of D. luscae (Beneden and Hesse) in average contraction is 0. 195 mm, its width is 0. 08 mm. The sizes of the larva of D. poUachii (Beneden and Hesse) are not indicated by Gallien, just as the other data, as a matter of fact, for he writes only about this larva that it completely similar to D. luscae (Beneden and Hesse). The length of the larva of D. denticulata (Olsson) is about 0. 35 mm whereas the width is 0. 15 mm. At the level of the beginning of the posterior quarter p. 199 of the body of the larva, the attaching disc begins, which occupies in length one-half of this quarter; the second half forms a powerful cone- shaped growth. The larvae of all species are devoid of eyes. Their pharynx is rounded and extends into a strongly developed sac -like intestine which sonnetimes extends posteriorly into the attaching disc. The excretory and other systems of organs were not discovered. The attaching armature consists of 12 hooks of the same type as among Mazocraes (Fig. 227); 10 edge hooks of approximately the same length and 2 larger 216 p. 200 T) o ^ n) m m 0) (U • iH f— 1 73 -d 1— < 4-> ^ -n u (J J.^., 1— t U o ■(-> (> (t o ID • r-4 Q O 3 ■-H 0) O 1— t c> (LI J5 Id • r-( 1—1 n) 14H U) C I— ( (U o 00 o 0) ni s o DO