102 VERTEBRATE ZOOLOGY 



Each kidney is made up of a mass of fine tubules, each of which 

 opens into the body cavity at one end, while the other end com- 

 municates with the Wolffian duct. This duct acts as a ureter. It 

 is a straight white tube which runs from the outer border of the 

 kidney to the dorsal wall of the cloaca. The urinary bladder is a 

 large bilobed sac, at the hinder end of the body cavity, which 

 springs from the ventral wall of the cloaca. Its opening into the 

 cloaca can be applied closely to the openings of the Wolffian ducts, 

 and it can thus receive the urine from them. 



On the ventral surface of each kidney is an irregular, yellow- 

 ish line which is called the adrenal body ; its function is unknown. 



Examine the ventral surface of the kidney with a hand lens 

 and note the minute openings of the urinary tubules. 



The genital organs consist of the testes in the male and the 

 ovaries in the female, and the ducts which conduct the genital 

 products to the outside. 



The Male. The testes are two yellow, ovoid bodies which lie 

 against the ventral surface of the kidneys and are attached to 

 the dorsal wall of the abdominal cavity by mesenteries. Joining 

 each testis with the ventral side of the kidney are about a dozen 

 fine tubules, the vasa efferentia, which are suspended in the mesen- 

 tery. Through these the spermatozoa, which are formed in the 

 testes, make their way into the kidney and thence into the 

 Wolffian duct. This duct thus serves the double function of a 

 ureter (an outlet for urine) and a vas deferens (an outlet for 

 sperm) ; it has on this account received a special name and is 

 called Leydig's duct. It is only in elasmobranchs and amphibians 

 that Leydig's duct is present. Along the hinder end of this duct 

 and connected with it by ducts is the seminal vesicle, a glandular 

 body in which sperm is stored during the breeding season. 



The Female. The ovaries differ very much in size and appear- 

 ance at different times of the year. In the springtime they are 

 often so distended with the small, spherical ova that they may 

 almost fill the abdominal cavity. If this is not their condition, 

 they appear as a pair of folded, dark-colored bodies which lie 

 on the ventral surface of the kidneys, attached to the dorsal body 

 wall by median mesenteries. The paired ducts through which 



