Reptilia. 



203 



is long and slender, and its bile sac is behind it. Not only 

 are the ovaries (and spermaries) and kidneys slender, but 

 they are not directly opposite each other ; in short, every- 

 thing is arranged on the tandem plan. Yet the snake is 

 bilaterally symmetrical, in its fundamental plan, like other 

 vertebrates and the vast majority of animals. 



Poisonous Snakes. Some of the front upper teeth of 

 these snakes, called " fangs, " are especially adapted for in- 

 troducing poison. They are longer than the other teeth, 



FIG. 126. DIAMOND RATTLESNAKE. 



From photograph by W. H. Fisher. From Recreation, by permission of G. O. Shields. 



can usually be erected or folded back, and have a hollow, 

 or groove, by which poison passes from the poison sac into 

 the wound by muscular pressure on the sac. The poison 

 gland is a modified form of salivary gland. This poison is 

 not a stomach poison, but a violent blood poison. Our 

 chief poisonous snakes are the rattlesnake, now becoming 

 rare in all thickly settled regions, the copperhead, and the 

 water moccasin of the South. Their abundance and the 

 danger from them are both grossly exaggerated. As an 



