428 COLLEGE ZOOLOGY 



The Urinogenital System. The dogfish shark possesses two 

 ribbcn-like kidneys (Fig. 359, K), one on either side of the dorsal 

 aorta. Their secretion is carried by small ducts into a larger 

 duct, the ureter (UD), which empties into a urinogenital sinus; 

 it then passes out of the body through the cloacal aperture (CL). 

 A series of yellowish gland-like bodies, called suprarenals, are 

 associated with the kidneys. 



The spermatozoa of the male arise in two testes and are car- 

 ried by the vasa deferentia into the urinogenital sinus. During 

 copulation they are transferred to the oviducts of the female 

 with the aid of the claspers. 



The eggs of the female arise in the single ovary (Fig. 359, OF), 

 which is attached to the dorsal wall of the abdominal cavity. 

 They break out into this cavity and enter the funnel-like open- 

 ings of the oviducts (OVD). When they reach an expanded 

 portion, called the omducal gland, they receive a horny covering 

 which protects them from injury after they are laid. 



2. ELASMOBRANCHS IN GENERAL 



The chief characteristics of the elasmobranchs are the presence 

 of a cartilaginous skeleton, a persistent notochord, placoid scales, 

 a spiral valve in the intestine, and claspers in the male ; and the 

 absence of a gill-cover or operculum, pyloric caeca, and an air- 

 bladder. The mouth is a transverse aperture on the ventral 

 side of the head. 



SUBCLASS I. SELACHII. There are two distinct types of 

 elasmobranchs belonging to this subclass: (i) sharks, which are 

 slender and cylindrical and have the gill-slits on the side; and 

 (2) rays, which are flattened dorso-ventrally and have the gill- 

 slits underneath. 



Order i. Squall. SHARKS AND DOGFISH SHARKS. The 

 sharks and dogfish sharks resemble in general the common horned 

 dogfish shark (Fig. 358). Most sharks are under eight feet in 

 length, and although carnivorous and voracious, very seldom 

 attack man. They feed principally on small fish, squids, and 



