WOLFFIAN DUCT AND BODY IN THE CHICK. 31 



in my sections of the Frog, but have completely failed to 

 find the earlier stages of this ingrowth. One would expect to 

 see it preceded by a thickening of the very flat cells lining the 

 body cavity at this point; one would hardly expect the flat 

 cells so specialised to form the lining of the body cavity of 

 the young larva suddenly, and without showing any change to 

 begin to grow inward. Eurther, if the cell cords described by 

 rtirbringer in the Salamander are really only rudimentary struc- 

 tures belonging to the anterior part of the mesonephros, as is 

 certainly the case in the Prog ; and if the process which FUr- 

 bringer describes for the posterior part of the mesonephros of 

 the Salamander takes place for all fully-developed parts of the 

 mesonephros, as is the case in the Frog, then part of the diffi- 

 culty caused by the peculiar secondary development of the 

 peritoneal funnels disappears. In other words, I believe Fiir- 

 bringer has made a mistake, precisely similar to that which was 

 made about the development of the Avian Wolffian body. He 

 has seen in the anterior part of a young larva the cell cords 

 mentioned above ; which were present at a time when there was 

 no trace of the posterior part of the mesonephros. He has also 

 seen in the hinder part of older larvae the blastema of cells 

 separate from the peritoneal epithelium from w^hich the Wolffian 

 tubules arise. Finally, he has connected these two conditions, 

 which are, as I believe, found in different regions of the trunk, 

 and has concluded that the cell strings of the anterior part have 

 separated from the peritoneal epithelium and given rise to the 

 cell masses of the posterior part which really develop indepen- 

 dently of the peritoneal epithelium, and eventually give rise to 

 the Wolffian tubules. 



My observations on Teleostei lead me, for similar reasons, to 

 assert an origin, in situ, of a continuous blastema, which later, 

 breaking up, will give rise to the Wolffian tubules. 



On the other hand, the older observers, including Vogt and 

 Rosenberg for Teleostei, Rathke, Johan. Miiller, Eeichert, Vogt, 

 for Amphibia,^ are quoted by Fiirbringer as asserting an origin 

 of the tubules as a series of excavations in a blastema of cells 

 lying just internal to the segmental (Wolffian) duct. And it 

 seems to me that the older observers were,^ as in their state- 

 ments concerning the development of the mesone{)hros in the 

 chick, not far from the truth. In the Sturgeon my observations 

 point to a similar conclusion ; in the just-hatched young a few 

 mesoblast cells are seen lying internal to the segmental duct. 

 These, at a later stage, are replaced by a more compact mass of 



^ ' Fiirbringer,' loc. cit., p. 46. 



' Ibid., loc. cit., p. 12. 



3 Self, • Quart. Journ. Mic. Sci.,' April, 1880. 



