492 TEXTBOOK OF ZOOLOGY 



dorsal rows of teeth. The mouth is made airtight by the shape and 

 fitting of the lips. The general portion of this cavity posterior to 

 the angle of the jaws is the pharynx. Well back in the floor of it, 

 is the tiny slitlike glottis in the midst of a slightly thickened laryngeal 

 prominence, the opening of which would receive only an object the 

 size of the head of a pin. The glottis leads into a recess called the 

 larynx and the two smooth-walled, saclike lungs extend posteriorly 

 from this. These saclike lungs have a fairly abundant vasculariza- 

 tion (blood supply). The air is pumped into and from the lungs by 

 the movements of the floor of the airtight mouth and change of posi- 

 tion of visceral organs within the body cavity. Branchial respiration 

 is accomplished largely by waving the highly vascularized external 

 gills back and forth in the water. The capillary branching of aortic 

 arches 4 and 5 provides most of this blood supply to the gills. The pul- 

 monary artery supplying the lungs is formed by a large branch from 

 aortic arch number 6. 



Urinogenital System 



The following organs constitute this composite system : a pair of 

 mesonephric kidneys, a pair of gonads (testes in male, ovaries in 

 female) numerous vasa efferentia from testes, one pair of Wolffian 

 or mesonephric ducts (ducts of Leydig in male), one pair of Miil- 

 lerian ducts or oviducts (in female, only vestigial in male) single 

 cloaca, the urinary bladder and the mesenteries (mesovarium, meso- 

 tubarium, and mesorchium). 



The kidneys are somewhat elongated and flat but thicker toward 

 the posterior, suspended in the dorsal peritoneum and lying dorsal 

 to the large intestine. The kidney of the female is smaller than 

 that of the male. The Wolffian duct leads from the lateral margin 

 of the kidney in either sex and proceeds directly from the posterior 

 portion of the kidney to make a dorsolateral entrance into the 

 cloaca. Inside the kidney the Malpighian corpuscles, including 

 glomeruli, are connected with the uriniferous tubules, which in turn 

 join the collecting tubules and they lead to the Wolffian duct. After 

 the urine enters the cloaca it collects in the urinary bladder which 

 hangs ventrally and serves as a storage reservoir. Upon becoming 

 filled with urine the bladder contracts and forces the urine back 

 into the cloaca and from here it passes to the exterior by way of 

 the anus. 



