164 
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. 
Kblliker’s view that the kidney of the Amniota is an 
organ sui 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 tubes in Elasmohrancliii . — 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 Elasmabranchs. 
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. Tlie intermediate cell mass was 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 Elasinobranch (Scyt- 
lium, Pristiurus, Torpedo) embryos, I found that the 
passage connecting the general body-cavity with that in the 
