402 METAZOAN PHYLA 



have been noted as being sources of food; and on the other hand one 

 type, the Gila monster, is poisonous. Crocodiles and alhgators are 

 feared in the countries in which they hve because of their attacks upon 

 persons going into the water, but they are valuable for the skins which 

 they furnish. None of the turtles is injurious, and some are useful as 

 food, being more often used in this manner than are any other reptiles. 

 Certain tortoises yield tortoise shell which is widely used commercially, 

 although it is now largely replaced by an artificial product. 



