80 ADAM SEDGWICK. 



dorsal position of the kidney is clearly a secondary change, 

 appearing only late in development, and due obviously to 

 the great size the kidney attains. Moreover, according to 

 Fiirbringer's view, one would expect to find some kind of 

 continuity between the developing kidney and dorsal part 

 of the Wolffian body ; but no trace of any such connection 

 can ever be seen. 



Finally, in view of the facts of development here recorded 

 for the chick, and of those about to be mentioned for Elas- 

 mobranchs, Braun's observations on the development of the 

 kidney blastema of Lizards from peritoneal ingrowths cannot 

 be accepted without further evidence. The irregularly 

 scattered cells lying between the Wolffian duct and the peri- 

 toneal epithelium, which Braun has figured, are by no means 

 proof of ingrowth of cells from the peritoneal epithelium. 

 Such an irregular arrangement of cells can be seen anywhere 

 adjoining the body-cavity epithelium. 



KoUiker's view that the kidney of the Amniota is an 

 organ sici generis, which was not present in any form in the 

 excretory system of the common ancestor of Icthyopsida and 

 Amniota, needs in my opinion no refutation ; for if true it 

 can only be established by proving all other hypotheses con- 

 cerning the kidney to be untenable. 



Development of segmental tithes in Elas77iohra7icliii. — I 

 should hardly have been bold enough to publish these obser- 

 vations on the development of the chick's Wolffian body, 

 opposed as they are "to statements supported by great 

 authority, had I not had the opportunity of examining the 

 early development of the parts in question in Elasinobranchs. 



I was thus enabled to confirm suspicions which I had 

 entertained since examining the development of the Wolffian 

 body of birds, as to the correctness of the description of the 

 earliest stages in these fishes. It is well known that the 

 Wolffian tubules of Elasmobranchii are derived from the seg- 

 mentally-arranged segmental tubes. These latter were said 

 to arise by an invagination, at first solid but subsequently 

 becoming hollow, of the peritoneal epithelium just internal 

 to the segmental duct into the cells of the intermediate cell 

 mass. The intermediate cell mass Avas said to be produced 

 by the coming together of the splanchnic and somatic layers 

 of that part of the body cavity, which at an earlier period 

 existed connecting the general ventral body cavity with the 

 dorsal continuations of it in the muscle plates. 



On examining specimens of young Ehasmobranch (Scyl- 

 lium, Pristiurus, Torpedo) embryos, I found that the 

 passage connecting the general body-cavity with that in the 



