EXCRETORY ORGANS 



379 



be called the ureter since it does not correspond to that tube in 

 mammals. This lies along the outer edge of the organ and passes 

 backward to open into the dorsal side of the cloaca. A watery 

 fluid, containing some of the solids of the blood, but not the 

 proteins, passes, under the blood pressure, through the thin wall 

 of the glomerulus into the capsule and so down the tubules. In 

 these it is deprived by reabsorption of some of its substances 

 (sugars and certain salts) which would be a loss to the body. 



t^^|^y ! o;;^ niBii m iii Lff ii u iiTii i i i ir ^ 



ar.t. 



Fig. 295. — A diagram of a kidney of the frog, to show the arrangement of the 

 tubules and blood vessels. One uriniferous tubule and a portion of the vascular 

 meshwork are shown separately. In reality the blood vessels entangle the 

 tubules. 



cap., Capillaries ; col.t., collecting tubule ; glom., glomerulus ; M.c, Bowman's capsule ; pe., peritoneum; 

 r.a., renal artery ; r.p.v., branch of the renal portal vein ; r.v., branch of a renal vein ; ur.t., uriniferous 

 tubule (somewhat unravelled ; note that its regions differ) ; ur.t'., places where other uriniferous 

 tubules open into the collecting duct ; W.d., Wolffian or kidney duct. 



and receives certain others, notably urea. It is then the urine, 

 and is stored temporarily in the bladder and voided at intervals. 



ORGANS OF REPRODUCTION 



The male organs of reproduction of the frog are the testes and 

 their ducts. The testes are a pair of ovoid bodies slung from the 

 surface of the kidneys by a fold of the peritoneum known as the 

 mesorchium. Each consists of a mass of seminiferous tubules, 

 in which the spermatozoa are formed. They communicate by 

 about a dozen small ducts, the vasa efferentia, in the mesorchium, 

 with the collecting tubules of the kidney, along which, and through 

 the Wolffian duct, the sperms pass to the cloaca, for the male 

 frog has not separate ducts for semen and for urine, but passes 

 these fluids to the exterior through the same passage. Each 

 Wolffian duct has attached to it a sac, the seminal vesicle, in 



