C1IORDATA 





change their color, although other genera of lizards can do this 

 to some extent also. They have two layers of pigment cells in 

 the skin; the more superficial is yellow, the deeper dark brown, 

 and the one or the other can become the more prominent accord- 

 ing to the will of the animal. 



Although most lizards live on the ground or in trees, son 

 prefer the water, either fresh or salt. They swim mostly In 

 the movement of their tails. Many are used for food, being 

 often over a meter in length, while they themselves are in some 

 cases herbivorous, in others carnivorous, often feeding on croco- 

 dile eggs. They are most abundant in Africa, Asia, and 

 Australia. The monitor of the Nile, a lizard two meters in 

 length, is very useful in destroying the eggs of the crocodile. 



Suborder 2. Ophidia 



The Ophidia (Gr. o<f>is, serpent) consist of the snakes, or ser- 

 pents. They are elongated reptiles, with a more or less cylin- 

 drical body covered with scales, which on the head are so 

 regularly and characteristically arranged as to be of systematic 

 importance. On the dorsal and lateral portions of the body 

 the scales are small; on the ventral side they are usually 

 rather broad plates extending completely across the ventral sur- 

 face, and thus forming a single series anterior to the cloacal 

 opening ; posterior to this opening there are two rows. These 

 ventral scales are called the abdominal scutes, and to them the 

 ventral ends of the ribs are attached. Appendages are absent 

 in the snakes ; only in a few species are there rudimentary pel- 

 vic limbs in the form of a pair of spinelike projections near the 

 cloacal opening. A pectoral girdle and sternum are always 

 absent, characteristics which distinguish the serpents from the 

 legless lizards. 



There is no tympanic membrane, so that the ear is very 

 rudimentary and the sense of hearing dull. They probably 

 notice the jar of an approaching animal. The senses of smell 

 and touch are, however, acute. There are no eyelids, as we 

 have already noted, but a transparent skin in front of the eyes. 

 In nearly all the snakes the bones of the mouth are not united 

 with one another immovably, but are connected by elastic Liga- 



