CLASS REPTILIA 



411 



or less hardened shell, are laid in the holes 

 dug by the female, in soil or decaying vege- 

 tation, in which heat aids in incubation. 



Nervous system 



The brain is more highly developed than 

 in the amphibians. The cerebral hemis- 

 pheres are larger, and a distinction can be 

 made between the superficial gray layer and 

 the central white medulla. The cerebellum 

 is also larger, indicating an increase in the 

 power of coordinating movements. There 

 are 12 pairs of cranial nerves. 



Sense organs 



The eye is small. It has a round pupil and 

 an iris which is usually dark in terrestrial 

 forms, but often colored in aquatic turtles. 

 The sense of hearing is not well developed, 

 but the turtle responds readily to vibrations 



through the skin, so it is easily frightened by 

 noises. The sense of smell enables the turtle 

 to distinguish between various kinds of food 

 both in and out of the water. The skin 

 over many parts of the body is very sensitive 

 to touch. 



OTHER REPTILIA 



Turtles 



Turtles live on land, in fresh water, or in 

 the sea. The word turtle is often applied to 

 semiaquatic species; tortoise, mainly or en- 

 tirely, to land species; and terrapin to certain 

 species that are edible and sold in markets. 

 Most of the land and fresh-water turtles hi- 

 bernate in the earth during the winter, but 

 in warmer countries they "sleep" ( estiva te) 

 during the hotter months. 



Some of the more interesting types of tur- 



Snapping turtle 



Painted turtle 



Figure 278. Common American turtles. The painted turtle is common in ponds. The snap- 

 ping turtle is less protected by shell than some turtles; it is well named for it is said that it 

 will snap as soon as hatched. 



ties are as follows. The snapping turtle 

 (Fig. 278) is famous for its strong jaws and 

 vicious bite. The musk turtle Sternotherus 

 emits a disagreeable odor when molested or 

 captured. The painted turtle (Fig. 278) is 

 brilliantly colored. The diamondback ter- 

 rapin Malaclemys (Fig. 279) is famous as 



food for man. The plastron of the box 

 turtle (Fig. 281) is hinged transversely near 

 the center so that the shell can be closed 

 completely when the animal is in danger. 

 The gopher tortoise Gopherus lives in bur- 

 rows in dry sandy areas of the southeastern 

 United States. Some of the giant tortoises, 



