340 



COLLEGE ZOOLOGY 



O Nonoxygenated o ^^^ To 

 blood 



# Oxygenated 

 blood 



Ventricle 



Atrium 



Sinus venosus 



venosus 



Ventricle 



AMPHIBIAN 



To body 



To body 

 To lungs 



From body 



Right 

 atrium 



Incomplete 

 partition 

 between 

 ventricles 



Left 

 ventricle 



REPTILE 



BIRD OR MAMMAL 



Figure 222. Diagrams showing the comparative structure and evolution of the heart among 

 different types of vertebrates; valves omitted. The arrows indicate the direction in which the 

 blood flows. 



drain wastes from the coelom. The nephro- 

 stomes in tadpoles are connected with the 

 uriniferous tubules, but they open into 

 branches of the renal vein in the adult. The 

 nephrostome mechanism for removal of 

 wastes probably represents a stage in the evo- 

 lution of the kidney. Urogenital arteries and 

 the renal portal vein (Fig. 221) bring blood 

 into the kidney. Blood leaves the kidney by 

 way of the renal veins. 



Reproductive system 



The function of the reproductive system 

 is the maintenance of the species from one 

 generation to the next. In the frog the sexes 

 are separate. The male can be distinguished 

 from the female by the greater thickness of 

 the first digit of his forelimbs (Fig. 209). 

 The sperms of the male arise in the testes 

 (Fig. 224), pass into the kidneys through 



