2O6 



THE BIOLOGY OF THE FROG 



CHAP. 



9 



nected with the collecting tubules which extend across the 

 dorsal side of the kidney to the ureter. The short tubes 

 which connect the longitudinal canal with the collecting 

 tubules widen out near the latter to form an ampulla. This 

 enlargement is formed by a Malpighian body which has lost 

 its glomerulus and consequently its original function. In 



Rana fusca there is a compara- 

 tively direct connection estab- 

 lished between the vasa effe- 

 rentia and the collecting tubules, 

 and the spermatozoa, therefore, 

 are not found in the Malpighian 

 bodies and functional renal tu- 

 bules. Bidder's canal occurs in 

 the kidneys of both sexes, but 

 its function in the female is not 

 known. 



In many of the lower verte- 

 brates (Elasmobranchs, Am- 

 phibia) the kidney is divided 

 into an anterior, or sexual portion, and a posterior, or ex- 

 cretory portion. The frog presents only the beginning of 

 such a differentiation. The vasa efferentia are connected 

 with the anterior part of the kidney, but the excretory func- 

 tion of this region is still retained. The course of the sper- 

 matozoa through the kidney varies considerably in different 

 species of frogs, as is evinced by the fact that it is much 

 more direct in Rana fusca than in R. esculenta. The latter 

 presents, doubtless, the more primitive condition. 



The kidney is supplied with blood from two different 

 .sources : (i) the renal arteries, which rise from the urino- 

 genital arteries, or direct from the aorta, and (2) the renal 

 portal veins, which convey venous blood from the posterior 



FIG. 56. Diagram to illustrate 

 the course of the spermatozoa 

 through the kidney of Rana 

 fusca. a, ampulla; c, collect- 

 ing tubule ; /, Bidder's longi- 

 tudinal canal ; /, uriniferous 

 tubule ; u, ureter ; v.e t vas 

 efferens. (Modified from 

 Beissner.) 



