384 MANUAL OF ZOOLOGY sect. 



has not only an auditory, but also an equilibrating function, 

 i.e., that the fish is enabled by its means to maintain its 

 equilibrium in the water. 



The kidneys (Fig. 227, k) are long flat lobulated 

 bodies lying one on each side of the backbone in the 

 posterior part of the abdominal cavity. From the ventral 

 surface of each spring numerous delicate ducts which unite 

 into a single tube, the ureter, opening directly into the 

 cloaca in the female, in the male into a small paired cham- 

 ber, the urogenital sinus {ug. s), which opens into the 

 cloaca (el). 



In the male dogfish the testes are a pair of large soft 

 organs situated in the body-cavity, and united with one 

 another posteriorly. From the anterior end of each arise 

 numerous delicate efferent ducts, which enter a long convo- 

 luted spermiduct or vas deferens (v. def) leading posteriorly 

 to the urogenital sinus. In the female there is a single 

 ovary suspended to the dorsal body-wall by a fold of peri- 

 toneum. In the adult it is studded all over with rounded 

 projections, the ova. There are two oviducts, a right and a 

 left, which extend along the whole length of the dorsal wall 

 of the ccelom below the kidneys. Anteriorly they unite 

 with one another below the gullet, and just in front of the 

 line and at the point of junction is a single aperture of con- 

 siderable size, by which both tubes communicate with the 

 ccelom ; posteriorly they open into the cloaca. About the 

 anterior third of each oviduct is narrow ; its posterior two- 

 thirds is wide and distensible, and at the junction of the 

 parts is a yellowish glandular mass, the shell-gland. 



Internal impregnation takes place, the spermatic fluid of 

 the male being passed, by means of the claspers, into the ovi- 

 ducts of the female. The ova, when ripe, break loose from 

 the surface of the ovary into the ccelom, and thence pass, 



