204 



THE BIOLOGY OF THE FROG 



CHAP. 



the ureter. The tubules are held together by connective 

 tissue which forms a support also for the numerous blood 



vessels with which the kid- 

 ney is supplied. 



The ventral surface of 

 the kidney is furnished 

 with numerous ciliated 

 funnels, the ncpJwos tomes, 

 whose expanded ends open 

 into the coelom. At their 

 other end the nephrostomes 

 empty into branches of the 

 renal veins, and the cilia 

 with which they are lined 

 beat toward the upper end 

 of these organs and thus 

 create a current of lymph 

 from the body cavity into 

 the blood. This relation 

 of the nephrostomes is a 

 peculiar one and occurs 

 only in the Anura. The 

 lower Amphibia preserve 

 the typical arrangement of 

 these organs, as the nephro- 

 stomes are connected with the renal tubules. This condi- 

 tion, as Marshall has found, occurs also in the early stages 

 of the Ufe of the frog, but later the nephrostomes lose their 

 original connection with the tubules and become united 

 secondarily with the renal veins. 



The kidney of the male frog stands in an intimate relation 

 to the sexual organs. The vasa effo-entia, or ducts which 

 convey the spermatozoa from the testis, pass into the sub- 



FlG. 54. — Diagram of a kidney show- 

 ing the ureter and collecting tubules. 

 C, collecting tubules ; Z, longitudi- 

 nal canal of Bidder; S, seminal 

 vesicle ; T\ testis ; U, ureter ; VE, 

 vasa efferentia. 



