THE GENESIS OF THE EGG IN TRITON. 265 



length of 1'4 cm., to consist of a string-like aggregation of 

 cells ("Gesclilechtszellen ") lying on the median side of the 

 Wolffian dnct, in the middle third of the body-cavity. These 

 sexual cells are at this time easily distinguished from neigh- 

 bouring cells by the presence of yolk elements, which have 

 elsewhere dissolved. They are invested with peritoneal 

 epithelium, which is entirely distinct and independent of 

 them. 



They begin now to multiply by division, and each cell 

 resulting from this division becomes separately invested in a 

 capsule of peritoneal cells. Meanwhile the yolk elements 

 have disappeared. About the time the hind legs bud forth, 

 the cells thus enclosed split up each into several cells, and 

 the nucleus in each of these several cells divides, producing 

 a small heap of nuclei. We thus arrive at a stage in which 

 a peritoneal capsule encloses several multinuclear cells. A 

 single nucleus in each of the sister cells enclosed in one 

 capsule now grows larger, while the others in the same cell 

 remain small, and take a peripheral position. The larger 

 nucleus with the protoplasm collected around it forms the 

 primordial ovum, while the smaller peripherally placed 

 nuclei, each invested with a share of the protoplasm of the 

 original cell, become the follicular epithelium. 



We have thus a peritoneal capsule enclosing several ova, 

 each of which is surrounded by its own follicular epithelium. 

 The concluding step in the formation of the young follicle is 

 brought about by ingrowths from the peritoneal envelope, 

 Avhich form a second envelope around each ovum. Each 

 ovum has now a membrana granulosa, having the same 

 origin as itself, and a tunica propria folliculi, which consists 

 of connective tissue derived from the peritoneal envelope of 

 the ovary. 



Nussbaum asserts that the same course of development is 

 found in the adult as in the embryo. He thus denies any 

 genetic relation between the peritoneal epithelium and the 

 primordial ova, claiming that both ova and follicular epithe- 

 lium are derived from " sexual cells," which are from begin- 

 ning to end distinct from the peritoneal layer. 



Dr. Valaoritis (9) has published a preliminary paper, in 

 which he has put forward a new theory of the origin of the 

 egg. He maintains that the ovum is at first a tvhite blood- 

 corpuscle (" Leucocyte "), which becomes lodged in the 

 ovarian epithelium, and here matures. 



In this paper he appears to base his conclusion concerning 

 the origin of the egg chiefly on the amosba-like power of 

 movement known to belong to white blood-corpuscles, and 



