Development of the Kidney in its relation to the 

 Wolffian Body in the Chick. By Adam Sedgwick, 

 B.A., Scholar of Trinity College, Cambridge ; 

 Demonstrator in tlie Morphological Laboratory. 

 (With Plates YI and YII.) 



This paper contains an account of observations on the 

 development of the excretory system of the chick, made with 

 a view of elucidating the relation which the kidney bears to 

 the Wolffian body. 



The Wolffian body in the embryo chick attains to a very 

 great development, but almost completely atrophies in the 

 adult, a small part only persisting in the male as part of the 

 testicular apparatus. 



In the embryos of lower Vertebrates, viz. most of the 

 Tcthyopsida, there is present, similarly, an organ called the 

 Wolffian body, which, however, much more completely 

 persists in the adult, functioning in part as kidney and in 

 part as semen carrier. 



The separation into an urinary part and into a sexual part 

 is much more complete in some forms than in others. In 

 the Elasmobranchii, for instance, the posterior part of the 

 embryonic Wolffian body gives rise in the adult to a well- 

 developed gland, the kidney, while the anterior part attains 

 a far less development ; in fact, more or less retrogrades in 

 the adult ; but in the male a part of it enters into connection 

 with the testis. 



In the Amniota the case is different. In them an embryonic 

 organ, called the Wolffian body, does not function at all in 

 the adult as an excretory organ ; it almost completely atro- 

 phies from its embryonic perfection, only a small part per- 

 sisting in the adult male as the epidydimis. The organ 

 which functions as kidney in the adult arises at a relatively 

 late stage, and is not apparently, as in Elasmobranchs, a 

 modified part of the hind end of the embryonic Wolffian 

 body. What, then, is the kidney of the Amniota ? Is it an 

 organ which has arisen de novo in the Amniota, or can it, by 

 a more accurate study of its development, be traced into 

 relation with the embryonic excretory system ? In other 

 words, can any evidence be obtained by the study of develop- 

 ment proving that the kidney of the chick phylogenetically 



