SURVEY OF VERTEBRATES 



123 



'toad.' Closely related to the true Lizards are the Chameleons, 

 famous for their ability to change color rapidly in response to 

 their surroundings. (Figs. 81, 82.) 



Snakes are essentially limbless Lizards in which even the in- 

 ternal supporting structures of the fore limbs have disappeared. 

 Most species of Snakes, in common with the great majority of 

 Vertebrates except the Mammals, are oviparous (egg-laying), 

 but a few are viviparous (bring forth 'living' young). And it is 

 hardly necessary to say that a few have poison glands associated 

 with special teeth, or fangs. The Rattlesnakes, Copperheads, 



A, Rattlesnake, Crotalis durissus; B, Cobra, Naja Iripudians 

 (From Newman, after Lydekker.) 



Water-moccasins, and Cobras are among the most notorious 

 in this respect. However, many species crush their prey as do 

 the Boa-constrictors, Pythons, and Kingsnakes. (Figs. 83, 230, 

 231.) 



D. Birds 



The Birds, constituting the class Aves, are the warm-blooded 

 (homothermal) animals that have made the air their own by the 

 development of fore limbs into wings, scales into an insulating 

 blanket of feathers, and other bodily adaptations. And not the 

 least of their progress is probably due to instinctive care of their 

 eggs and young. That Birds are an offshoot from the Reptilian 

 stock, probably the Dinosaurs, is attested by the fossil remains 

 of a Bird, known as Archaeopteryx, with characteristic feathers 

 but lizard-like tail and teeth. (Figs. 232, 233.) 



The Birds to-day form a remarkably homogeneous group, prob- 

 ably due to restrictions imposed by the mechanical problems in- 



