STUDIES ON SEX IN CREPIDULA 33 



scattered granules. Part of it, however, containing the folUcle 

 nuclei, concentrates about the germ cells (fig. 49). 



It is of interest at this point to refer to the observation of 

 Buresch ('11) on the hermaphrodite Pulmonate, Helix arbus- 

 lorum. Tins animal passes from a male to a female condition 

 and during the transition period there is a series of marked de- 

 generative changes in the gonad as there are in Qrepidula plana. 

 The process is very different, however, from that in Crepidula ; in 

 Helix arbustorum not only the male germ cells, but also the 

 germinal epithelium and the follicle cells break up and are 

 destroyed. The oocytes are then already in the resting or 

 growth stages and the destruction of the germinal epithelium 

 throws them into the lumen of the gonad, where they take up 

 the dissolving cell elements as food and thereby grow rapidly. 

 They then make their way to the uterus, meanwhile undergoing 

 the maturation divisions. 



In Crepidula plana the germinal epithelium, instead of being 

 destroyed as in Helix, becomes thicker and more prominent than 

 it has been during the male phase, and the follicle cells are more 

 numerous than ever before. 



B. Development of the ovary. In a large degenerate male, the 

 beginning of female differentiation may begin immediately after 

 the changes which we have been considering. As the primitive 

 germ cells assume their characteristic appearance in the ger- 

 minal layer, the primordial egg cells exceed the primordial sperm 

 cells in number, and the nuclear pattern of the former becomes 

 more distinct (fig. 49) than it has been at any time since the 

 young testis was in the early stages of development. Follicu- 

 lar nuclei are present in large numbers. Whether the excess of 

 primordial female over primordial male cells at this time is due 

 to multiplication of the former or disappearance of some of the 

 latter, or to both, is not certain; for since the number of eggs is 

 very small compared to the number of- sperm, the number of 

 oogonial divisions is also very small and the mitotic figures are 

 hard to find. It is certain, however, that from the stage of 

 figure 49 on, periods of oogonial division may occur at inter- 

 vals, and some of the material has fortunately been fixed while 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, YOL. 23, NO. 1 



