ox THE DEVELOrMENT AND SHAPE OF UEINIFEROUS 

 TUBULES OF CERTAIN" OF THE HIGHER MAMMALS. 



BY 



G. CARL HUBER. 



From the Histological Laboratory of the University of Michigan. 



With 24 Figures. 



As is well known, the excretory system of the amniota develops as a 

 series of distinct organs, the pronephros, the mesonephros, and the nieta- 

 nephros. The pronephros, which is the first excretory organ to difEer- 

 entiate, and is also phylogenetically the oldest, disappears in all amniota; 

 its consideration is here dispensed with. The mesonephros, which func- 

 tionates throngliont life as the chief excretory organ of anamnia, is an em- 

 bryonic organ in amniota, in which it disappears as an excretory organ 

 and is replaced by the permanent or true kidney, the metanephros. The 

 development of the metanephros is, however, so closely related to that of 

 the mesonephros, in both its phylogeny and ontogeny, that a consideration 

 of the development of the former will to some extent necessitate a con- 

 sideration of the development of the latter. This will be done only so far 

 as necessary, as a consideration of the development of the mesonephros 

 will not form a part of this contribution. 



Our present day conception of the anlage and development of the meta- 

 nephros dates from Kupffer's contribution based on observations made on 

 sheep embryos. In an embryo 8 mm. in length he fqund that from the 

 dorsal wall of the Wolffian or mesonephric ducts near their posterior ter- 

 mination, there is formed an evagination whicli he designated as the 

 " Nierenkanal." These buds, one of which appears in connection with 

 each ^^'olffian duct, grow dorsally and cephalad and, as observations on 

 older emlu'yos revealed, become associated with the development of the 

 permanent kidney. Anticipating these observations, we find those of 

 Remak and Kolliker, who recognized these buds, but traced their origin 

 to the cloa-ca or bladder, and of still earlier date the observations of 

 Rathke, who recognized a blastema situated between the dorsal wall of the 

 embryo and the mesonephros in wbich the kidiu\v liad its origin and from 

 wliieh the ureters were supposed to grow toward tlie l>hidd(M-. That the 

 American .TotRNAi. of Anatomy. — Sii'im.k.ment to Vol. IV, June 1, 1905. 



