8 INTRODUCTION TO THE CLASS OF REPTILES 



also true of some large species of serpents, such as the great 

 constrictors of India and South America. 



Distribution. — Reptiles reach their maximum develop- 

 ment in the tropics and the subtropics, between the isother- 

 mals of 32° F. North and south of that zone, reptilian life 

 still is abundantly represented, but chiefly by small species. 

 The largest land serpents are found in the low-lying, moist 

 and hot forests of the equatorial regions; but crocodilians of 

 the largest size are found several hundred miles from the 

 Equator, both north and south. The largest tortoises live 

 close to the Equator. 



Poisonous Species. — Among our reptiles only one lizard 

 and a few species of serpents are venomous — an exceedingly 

 small proportion of the whole number. Indeed, so few in 

 number are the dangerous species of North America, it is an 

 easy matter for any intelligent person to learn to recognize 

 all of them at sight. In a few hours of diligent and conscien- 

 tious study, aided by a text-book that has been properly 

 designed, any clear-headed person over fourteen years of age 

 can learn to determine almost at a glance whether any fully 

 grown serpent of North America is poisonous or harmless* 

 This is possible from the fact that more than half of the ven- 

 omous species possess rattles, and those which have not are 

 few in number. 



Useful Species. — Many reptiles are of decided value to 

 mankind, by reason of the rats, mice and other destructive 

 vermin which they destroy. Others diligently devour in- 

 sects. Quite a number furnish useful food, and some yield 

 skins and other commercial products of much value. 



