STUDIES ON SEX IN CREPIDULA 31 



spermatogonia no longer stain like living cells (fig. 42). It will 

 be recalled (p. 17) that in the immature animal when male 

 development does not immediately follow the production of 

 spermatogonia which are set free in the lumen, they may de- 

 generate and form amorphous bodies (fig. 1). The process 

 during degeneration of the testis is the same. 



The testis now contain only spermatids, sperm, and degen- 

 erate cells which are mostly spermatogonia. A few spermato- 

 cytes degenerate, but the majority complete the maturation 

 divisions. The spermatoblasts and some of the spermatosomes 

 of the atypical series suffer the same fate as the spermatogonia; 

 but the majority of the later stages must complete their develop- 

 ment, for only a few late spermatosomes are found degenerating. 



In the meantime the transformation of the spermatids into 

 spermatozoa, the passage of these into the seminal vesicle, and 

 the shrinkage of the testis, continue. Eventually the gonad 

 shrivels until nearly all the follicles are drawn in and the main 

 sub-divisions of the organ remain as strands reaching here and 

 there in the visceral sac, retaining their connection with one an- 

 other. During the reduction, part of the connective tissue sheath 

 is cast off into the perivisceral spaces. 



During the shrinkage, marked changes have taken place around 

 the periphery of the gonad. The reduction in size brings the few 

 widely scattered cells found next the connective tissue sheath 

 in the male phase, close together so that they form a continuous 

 layer. This layer consists of primordial egg and sperm cells 

 and follicle cells. Once more we have a follicular syncytium in 

 which the germ cells are embedded. The chemical changes 

 attendant upon the dissolution of the testis cells at this time seem 

 to affect the primordial germ cells and make them harder to 

 identify (figs. 44, 45). It has been said that during the male 

 phase the primordial egg cells are changed in appearance, and 

 this is true of the period of regression. The primordial sperm 

 cells are also hard to distinguish. Their nuclei become dis- 

 torted, as are those of the follicle cells, and conditions in general 

 are hard to interpret. Some of the primordial germ cells of 

 both types are, however, always distinguishable and there is no 



