526 COLLEGE ZOOLOGY 



plates on the dorsal surface of the skull and often on other 

 parts of the body. Some of the Stegocephalia are called 

 Labyrinthodonts because the dentine of their teeth is much 

 folded. 



Microsauria are small extinct animals probably belonging 

 to the Amphibia, though they are often placed with the reptiles. 



The Economic Importance of the Amphibia. — The Amphibia 

 are practically all beneficial to man. Many of them are so rare 

 as to be of little value, but the frogs and toads are of consider- 

 able importance. Frogs have been and are now used extensively 

 for laboratory dissections and for physiological experiments and 

 investigations. They seem in fact to have been " especially 

 designed as a subject for biological research." 



Frogs' legs are eagerly sought as an article of food. New 

 York, Maryland, Virginia, Indiana, Ohio, Missouri, and Cali- 

 fornia furnish the largest number for market. Frog hunters 

 obtain an annual price of about $ 50,000 for their catch. " Frog 

 farms " are now carried on profitably in Wisconsin, California, 

 and several other states. Small frogs are often used as fish 

 bait. 



Frogs and toads are widely recognized as enemies of injurious 

 insects. The toads are of special value, since they are accustomed 

 to live in gardens where insects are most injurious (see p. 510)- 

 In France the gardeners even buy toads to aid them in keeping 

 obnoxious insects under control. 



