3o4 



ZOOLOGY 



purified, and the pure blood in the ventricle, mingled with 

 some venous blood, goes to the aortas {RAo, LAo), and so 

 on to the trunk and head. Thus, in the turtles, the body 

 receives a little impure blood, and this fact results in keeping 

 down the temperature of the body. 



The organs of respiration are a pair of large lungs. These 

 show a great advance over those of the frog, since they are not 

 mere sacs, but contain many lobules. As the body is encased in 



an inflexible shell, the 

 lungs cannot be filled bj' 

 raising the ribs, as is the 

 case with us, and so the 

 turtle seems to depend 

 largely upon the move- 

 ments of its capacious 

 throat to force air into or 

 from the lungs. Certain 

 water tortoises have 

 great sacs opening from 

 the cloaca, whose walls 

 are filled with blood-vessels, and which may be alternateljr 

 filled with and emptied of water through the cloacal opening. 

 The oxygen of the fresh water is absorbed by the l^lood-vesscls 

 in the wall of the sac. Thus these sacs are like gill chambers 

 in some lower animals, and enalile the turtles to breathe 

 even while submerged. However, this device is only a tempo- 

 rary expedient and cannot long replace respiration by the lungs. 

 The organs of excretion and reproduction. — The kidneys 

 are small and round, in marked contrast to those of amphibi- 

 ans, of which, indeed, they represent only the posterior por- 

 tion. They are, on the other hand, like the kidneys of the 



iny «■ 



Fig. 3.33. — Side view of the brain of a turtle 

 (Emj^s). 1, olfactory' nerve; //, oijtic 

 nerve ; hoi, lobe of smell ; VH , eerebral 

 hemispheres ; MH, optie lobes ; Tro, 

 "optic tract"; HH, cerebellum; NH, 

 medulla; 7?, spinal cord; //?/, "infundi- 

 bulum " terminating in the " h>-poph}'sis." 

 From Wiedersheim, " Comp. Anat." 



