204 ANIMAL STUDIES 



carnivorous, and usually very voracious. The lizards espe- 

 cially devour large quantities of insects and snails, together 

 with small fishes and frogs. The latter figure largely in 

 the turtle's bill of fare, and in that of the snakes, which 

 also capture birds and mammals. On the other hand, many 

 of the reptiles prey upon one another; and they are the 

 favorite food of hawks and owls and numerous water-birds, 

 of skunks and weasels and many other animals, which look 

 for them continually. Many of the turtles, owing to their 

 protective armor, and the snakes because of their poison- 

 ous bite or great size and strength, are more or less ex- 

 empt, but this is not true of their eggs and young. The 

 smaller species depend upon keenness of sense, agility, and 

 inconspicuous tints. These latter may undergo changes 

 according to the character of the surroundings, but usually 

 only to a slight extent. The chameleons of the tropics 

 and a similarly colored green lizard on the pine-trees in 

 the Southern States are able to change with great rapidity 

 from green, through various shades, to brown. 



191. Respiration and circulation, While still in the egg 

 the young lizard develops rudimentary gills, and thus bears 



FIG. 119. Dissection of lizard (Sceloporus). an., anal opening ; au., auricle ; crb.h,, 

 brain; coec., intestine; kd., kidney; Ling., left lung; lr., liver; pn., pancreas ; 

 sp.c., spinal cord ; spl., spleen ; st., stomach ; v., ventricle of heart. 



evidence to the fact that its distant ancestors were aquatic ; 

 but before hatching they disappear, and lungs arise, which 



