. n: I in: MiiMiu: .U:M \.\\ u:. 



The further fate of the piimiti\e kidney i- very different in the 

 M-ji.-i! BBOf \'er< lii the Aii;imni;i. /.., in r'Mie< Mini 



Amphibia, it becomes the permanent urinary organ, through which 

 'ions nt' the body are eliminated ; hut b^ide- that, it also 

 acquires iclatious ID tin- >cxual apparatus UJH.M wliich, however, I 

 shall not mlrr until later. In I'.irds and Mammals, mi t he contrary, 



iln- primitive- kiilney is functional onl\ a >ln-rt time during embryonic 



lit'e ; soon after its e-tahii>hmcnt it undergoes profound regr 

 changes, and at laM is preserved only in part, in ><> far as it enteiCl 

 into the >er\ ice of the sexual appiratus. and, a-> we >liall likewise see 

 later, participates in conducting away th-- sexual pn-dn 



(c) The Kidney. (Metanephros.) 



Tho secretion of urine is assumed in the higher Vertelrates by 

 a third inland, which is established at the posterior end cf the meso- 

 uephric duct the permanent ; /. /'////'//. The method of its formation, 

 M -lii.-h apj >ears to differ at lirsfc from that of the mesonephros, presents 

 u'reat. obstacles to its investigation. It i> must accuratelv known 

 from studies on the development of the Chick through the works of 

 S'EDGWICK. At the beginning of the third day of incubation m the 

 < 'hick there grows out of the [posterior] end ot the moonephric duct, 

 from its dorsal wall, an evaluation the wn-fiiri/ >fct <>/ t/n- /, / 

 <>r ",'eter. 



There are two conflicting views relative to its connection with the 

 development of the kidney. According to the older view, which is 

 still shared by many, the kidney is formed from the ureter in the 

 manner of an ordinary glandular growth. It is maintained that 

 evagination> take place which give rise to other ovaginations, and 

 thus produce the whole parenchyma of the kidney. According to the 

 second view, which has been formulated especially by the more recent 

 ombryologists, by SEMPER, BRAUN, FUI:I:I:IM;I:!J. SI:H.;WICK, and 

 ].\i.FOUR, the permanent kidney is, on the contrary, developed out 

 of two different fundaments, which come into relation with each other 

 only secondarily: the medullary substance \\ith its collect ing tubules 

 out of the ureter, the cortical substance with the tortuous tubules 

 and the loops of HENLE, on the other hand, out of a special fundament. 

 According to this view there would be an agreement between the 

 development of the kidney and primitive kidney, in as far as in the 

 latter the mesonephric duct and the mcsonephric tubules also arise 

 separately, and only secondarily enter into relation with each other 



