REPTILIA. 385 



that the purest blood goes to the brain and the least pure to 

 the lungs (see Fig. 168). Two aortic arches unite, giving rise 

 to the dorsal aorta. In the reptiles and higher groups of 

 vertebrates the renal-portal circulation (see Fig. 178, r.p.) 

 ceases to be of much importance, but the hepatic portal is 

 increasingly important. The red corpuscles are elliptical and 

 possess nuclei. 



412. Nervous System and Special Sense Organs. The 

 brain is not large in the reptiles, but is rather more highly 

 developed than in the Amphibia. This is especially true of the 

 cerebral hemispheres. The usual senses are represented. The 

 rather larger eyes are provided with movable eyelids except 

 among the snakes, in which a permanent transparent membrane 

 covers the eye. In some reptiles (lizards) there is a remnant 

 of a median eye which is hopelessly degenerate in the adult. 

 It is in connection with the pineal body in the second division 

 of the brain. 



413. Habits. The reptiles are best represented in the 

 tropical regions. The larger types, as the crocodiles, python, 

 boa are almost confined to the warm zones, especially of South 

 America, Africa and Asia. Numerous smaller representatives 

 of the lizards, snakes, and turtles are found in temperate lati- 

 tudes. These usually undergo a period of hibernation during 

 the cold season. This habit of hibernating and seeking warmer 

 climates seems related to the cold-blooded condition. The heat- 

 producing qualities of the animals are not equal to the task of 

 maintaining activity during extreme cold. The variation of 

 temperature is of course a more serious problem to terrestrial 

 animals than to aquatic types. Although air-breathers, very 

 many of the group are aquatic, as the turtles, crocodiles, and 

 many snakes. The lizards are almost without exception terres- 

 trial. Nearly all prey on other animals ; the smaller on worms, 

 insects, and eggs of various kinds, and the larger on birds, 

 fish, amphibia, and mammals. The land tortoises are vege- 

 table feeders. 



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