THE GENESIS OF THE EGG IN TRITON. 267 



the germinal epithelium is distributed in small islands, and 

 the stroma cells come to the surface of the ovary, where 

 they take the form of endothelium. The primordial eggs 

 then arise by a (further) growth of single cells of the 

 germinal epithelium, while the enlargement of the ovary 

 results from the growth of the stroma." 



Valaoritis (1. c, p. 598) states that these islands are 

 wanting in immature specimens of aS*. maculata, and that 

 the period of sexual activity is distinguished from that of 

 inactivity only by the presence of such islands. 



Hoffman (according to Valaoritis) says that " the peri- 

 toneal epithelium, which covers the ovary of the land 

 Salamander, is interrupted in places, in which places there 

 is an ovarian epithelium, which serves to replace the eggs 

 that have been used." 



From these citations it is apparent that great differences 

 of opinion exist with reference, not only to the precise 

 origin of the primordial ova, but also to the character of 

 the external cell-layer of the ovary. 



In regard to the origin of the ovum, we have at least three 

 quite different theories. While differing in regard to the 

 mode of origin, the majority of authorities maintain that 

 the ova are derived from the outer cell-layer of the ovary. 

 On the other hand, Nussbaum holds that they arise entirely 

 independently of this outer layer — from so-called " Gesch- 

 lechtszellen." 



Valaoritis agrees with Nussbaum in denying the epithelial 

 origin of the ovum, but claims that it is nothing but a white 

 blood-corpuscle. 



The difference of opinion in regard to the character of the 

 outer cell-layer of the ovary has led to confusion in the 

 names applied to it. Some call it '^ peritoneal epithelium ;" 

 some " endothelium ;" while others hold that it is made up 

 of two distinct elements, which they distinguish as " epi- 

 thelium" and '^endothelium." In this paper it will be 

 spoken of as " germinal epithelium." I began the investi- 

 gation of this point in company with a fellow-student, Mr. 

 Sasaki, to whom I am indebted for a few figures, which he 

 has generously allowed me to use. We have made together 

 a very large number of silver nitrate preparations for surface 

 views, extending through the winter and spring months ; 

 and also many sections. Our experience has taught us, what 

 others have learned before us, how difficult a matter it is to 

 determine the origin of the ovum. Our studies are not as 

 complete as they might have been, had we not been com- 

 pelled to drop them at an early date in order to prepare for 



