THE REPTILES OF 

 WESTERN NORTH AMERICA 



INTRODUCTION 



The term reptile is popularly applied to all cold-blooded 

 vertebrates other than fishes. Thus used, it includes two 

 groups of animals which differ in many important respects. 

 These are the amphibians and the reptiles proper j the 

 former more closely allied to the fishes 5 the latter, to the 

 birds. 



The typical amphibians, such as most frogs, toads, sala- 

 manders, and newts, lay their eggs in the water, and the 

 young, for a time, breathe by means of gills, very much as 

 do the fishes. Later on, they undergo a metamorphosis, 

 during which the gills and other larval characteristics dis- 

 appear, the tadpole assumes the form and structure of its 

 parents and emerges from the water to breathe air and 

 spend a greater or less portion of its life on land. The 

 skin of our amphibians is not provided with scales, but is 

 smooth or warty, very glandular, and often covered with a 

 slimy secretion. 



The true reptiles, such as alligators, turtles, lizards, and 

 snakes, on the other hand, never lay their eggs in the water, 

 even the marine species coming to land for this purpose. 

 Their young never breathe by means of gills, but are 

 hatched or born with the form and structure of the adult. 

 The skin, except of some turtles, is covered with scales, and 

 is dry, never slimy. 



There are, also, many anatomical and embryological dif- 

 ferences between the two classes, but these need not be 

 stated here. Our reptiles and amphibians may be distin- 

 guished by the following 



