STUDIES ON SEX IN CREl'IDULA 29 



gonia are forming in large numbers they make a complete ger- 

 minal layer at the outside; but in less active testes the connective 

 tissue sheath may be almost bare of cells, although all stages of 

 spermatogenesis are present in the interior. At intervals along 

 the sheath, however, there are always a few primordial male 

 cells, a few follicle cells, and a few primordial female cells, at- 

 tached to the connective tissue. 



Follicle cells do not seem to be functional during the male 

 phase, for they do not multiply in sufficient numbers to keep pace 

 with the growth of the gonad during male development. In the 

 very young specimen (figs. 1, 2, 3) and in the sexually inactive 

 animals (fig. 50), the follicle nuclei are everywhere present in the 

 germinal layer. The cytoplasm belonging to them is great in 

 relation to the size of the nucleus, and is extended along the 

 connective tissue sheath ; in this layer of cytoplasm the true germ 

 cells are embedded. No cell boundaries can be seen between the 

 follicle nuclei; the latter often lie curved about the germ cells. 

 It is evident that during the rapid extension of the gonad to 

 form the testis, the follicle cells do not divide as fast as the 

 others, since they are present in so few numbers in the adult 

 male. Just what element of the testis does furnish the nourish- 

 ment of the developing sperm cannot be stated. It might be 

 suggested that the degenerating apyrene spermatosomes have 

 some such function, in view of Reinke's ('12) comparison be- 

 tween the apyrene sperm of Strombus and the nurse cells of 

 other Molluscs; but in Crepidula the spermatozoa are never 

 gathered about any cell in the testis. They do not remain in 

 the follicles long after they have become adult, but find their 

 way at once into the seminal vesicle. 



The primordial egg cells are also much less numerous, rela- 

 tively, than they have been at any time previous to the adult 

 male phase. They occur occasionally, either in the form pre- 

 viously described, or in a more faintly staining condition in 

 which the chromatic bodies are hard to distinguish. In figure 41 

 are two which are so greatly changed that if it were not for 

 transitional forms they could not be identified as primordial egg 

 cells. The figure does not show how much they differ in stain- 



