1879.] in its relation to the Wolffian body in the chick. 295 



cord or blastema of cells, the development of whicli I have just 

 described, and which I have traced into relation with the de- 

 veloping ureter, gives rise not only to the vascular and con- 

 nective tissue elements of the kidney, but also to the epithelium 

 of the secretory tubules. 



The fact which my observations have brought out most 

 clearly, and on which I wish most strongly to insist, is this — The 

 cells from which the kidney tubules arise are developed con- 

 tinuously and contemporaneously with the cells from which the 

 tubules of the Wolffian body arise. It is hardly necessary to point 

 out the important bearing of this fact on any hypothesis as to the 

 phylogenetic origin of the kidney. It obviously points most 

 decisively to the conclusion that the kidney is the posterior part 

 of the Wolffian body, which has become separated from the 

 latter, and thrown back in its later development. 



Three views have been held concerning the origin of the 

 kidney in the Amniota. 



1. That it is the posterior part of the Wolffian body. 

 (Balfour \ Semper^, Braun^.) 



2. That it is derived from secondary dorsal posterior tubules 

 of the Wolffian body. (Fiirbringer*.) 



3. That it is a structure sui generis which has no representa- 

 tive in the Ichthyopsida. (Kolliker.) 



Balfour some time ago put forward the hypothesis that the 

 kidney of the Amniota was the posterior part of the Wolffian 

 body, and he compared it to the posterior part of the Wolffian 

 body of Elasmobranchs, which reaches in the adult a much 

 greater development than the anterior part, and opens by separate 

 ducts into the cloaca. He supposed that in both cases the great 

 development of the posterior part of the Wolffian body and its 

 separation from the anterior part were due to the same cause, viz. 

 the relation which the anterior part has entered into with the 

 testis and the consequent loss of its excretory function, so that all 

 the work of excretion was thrown upon the posterior part. 



This view, arrived at by Balfour from theoretical considerations, 

 my own observations on the chick completely confirm. Braun, 

 who holds the same view as to the homology of the kidney of 

 Amniota, has supported it by his observations on the development 

 of the kidney in the Lizard. 



But his observations equally well bear another interpretation, 

 and have been used by Fiirbringer in support of his view that it 



^ " Urogen. organs of Vertebrates," Journal of Anatomy and Physiology, Vol. x, 

 2 " Urogenitalsystem der Plagiostomen," Arheiten, Vol. ii. 



* " Ueber Entwickeluug des Urogenitalsystems der einheimischen Keptilien." 

 Verh. d. phys.-med. Gesellschaft zu Wiirzburg. 



* MorplwJog. Jahrbuch, Bd. 4. 



