2 7 o ECONOMIC ZOOLOGY AND ENTOMOLOGY 



the snake strikes, these fangs are lowered and thrust into 

 the victim and the poison, which is secreted by small glands in 

 the head, is injected through them. There are several species 

 of rattlesnakes, all belonging to the genus Crotalus. They are 

 most abundant in the Southwest, but are found in almost all 

 parts of the United States except in the higher mountains. 

 The rattle on the tail is composed of a series of partly overlap- 

 ping thin horny pieces, the somewhat modified successively 

 formed epidermal coverings of the tip of the body. A new rattle 

 is added each time the snake sheds its skin, and as the snakes 

 usually molt about three times a year the age of a rattlesnake 

 may be approximately estimated provided none of the terminal 

 units of the rattle has been lost. 



FIG. 124. The rattles of the rattlesnake. The lower figure shows a longi- 

 tudinal section of the rattle. 



The chestnut-colored copperheads, Agkistrodon contortrix, 

 occur throughout the eastern and middle United States. They 

 are very vicious and dangerous, striking without warning. 

 The water-moccasin, Agkistrodon pisciwris, of the southern 

 states is the most dangerous of our serpents. It is found in 

 swampy places and in the water. It is ill-tempered and aggres- 

 sive, striking on the slightest provocation. The poisonous 

 harlequins or coral-snakes, Elapsfulvius, that live in the south- 

 eastern United States, are also very venomous. They are 

 black, very strikingly marked by broad, yellow-bordered, 

 crimson rings. 



