GENERATIVE ORGANS. 



747 



though with reference to certain stages in the history further 

 researches are still required 1 . 



In Elasmobranchii the male germinal cells, instead of remain- 

 ing in the germinal epithelium, migrate into the adjacent stroma, 

 accompanied I believe by some of the indifferent epithelial cells. 

 Here they increase in number, and give rise to masses of variable 

 form, composed partly of true germinal cells, and partly of 

 smaller cells with deeply staining nuclei, which are, I believe, 

 derived from the germinal epithelium. 



FIG. 411. TRANSVERSE SECTION THROUGH THE OVARY OF A YOUNG EMBRYO 

 OK SCYLLIUM CANICULA, TO SHEW THE PRIMITIVE GERMINAL CELLS (po) LYING 

 IN THE GERMINAL EPITHELIUM ON THE OUTER SIDE OF THE OVARIAN RIDGE. 



These masses next break up into ampullae, mainly formed of 

 germinal cells, and each provided with a central lumen ; and 

 these ampullae attach themselves to tubes derived from the 

 smaller cells, which are in their turn continuous with the 

 testicular network. The spermatozoa are developed from the 

 cells forming the walls of the primitive ampulla;; but the 

 process of their formation does not concern us in this chapter. 



In the Reptilia Braun has traced the passage of the primitive 

 germinal cells into the testicular tubes, and I am able to confirm 

 his observations on this point : he has not however traced their 

 further history. 



1 Balbiani (No. 554) has also recently dealt with this subject, but I cannot bring 

 my own observations into accord with his as to the structure of the Elasmobranch 

 testis. 



