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 



