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 



