STUDIES ON SEX IN CREPIDULA 47 



Ancel ('03) on Helix pomatia are among the best known and 

 most fully developed investigations which have been made. 

 Ancel beheves that there is a true indifferent germinal epithe- 

 lium in Helix, whose cells are capable of differentiation into 

 indifferent sex cells or into nurse cells. The indifferent sex cells 

 may develop into spermatogonia or oogonia according to the 

 conditions of the environment. I quote the following from his 

 conclusions : 



. . . . une cellule progerminative indifferente deviant male ou 

 femelle suivant les conditions qu'elle rencontre dans la glande genitale 

 au moment de son apparition, conditions reglees par la transfoimation 

 d'un certain nombre de cellules epitheliales en elements nourriciers 

 61aborateurs d'un material special. 



Demoll ('12 b), on the contrary, working on the same species 

 as Ancel, finds the first differentiation of the male and female 

 sex cells to take place at a time when a Nebenkern appears in the 

 cytoplasm, more marked in the male cells than in the female. He 

 concludes that the differentiation of the Nebenkern determines 

 the character of the germ cell, which may be considered indif- 

 ferent up to this time. He further concludes by analogy with 

 dioecious animals in which the sex is determined by the acces- 

 sory chromosome, that a chromosome difference is responsible 

 for the differentiation of the Nebenkern. 



Buresch ('11), working on Helix arbustorum, agrees with 

 Ancel that the male and female germ cells are determined as such 

 by the presence or absence of nurse cells. He does not find, as 

 Ancel does, that there is a stage of spermatogonial development, 

 then nurse cell development, then oogonial development; but 

 that all the different elements of the gonad are being developed 

 simultaneously. 



In his ''Germ Cell Cycle" Hegner has reviewed these and 

 other works on the germ cells of hermaphrodites. It is not neces- 

 sary to repeat Hegner's review of hermaphroditism in animals 

 other than Molluscs, except possibly to call attention to the 

 investigations of Boveri ('11) and Schleip ('11) on the germ 

 cells of the hermaphrodite Nematode Rhabditis nigTovenosa, in 



