INTRODUCTION. XXXI 



prominences, which give them a fantastic appearance. The hearing is very 

 quick. The tympanic membrane is generally exposed on the side of the 

 head, and in certain species is very large. In Opisthoglossa the tongue is 

 used in capturing the prey. Most often it is attached in front, and the 

 hinder portion can be thrown forward out of the mouth ; when not so free 

 the whole tongue is pushed forward. The food consists of worms, insects, 

 etc., and occasionally of small vertebrates. Several large species are said 

 to catch fish. The latter, however, are well able to retaliate, and the 

 batrachians furnish food for numbers of the fishes. A large number of 

 the species have voice. A special apparatus for its production, possessed 

 by the males, consists of a pair of membranous gular sacs, sometimes a 

 single one, under the floor of the mouth, with which they communicate 

 by a couple of slits. These sacs are either covered by the skin or, in a 

 few instances, there are openings through which they are protruded when 

 inflated with air from the lungs. The largest species of the order is the 

 Marine Toad, Bufo agua, of South America; the largest North American 

 is the Bull Frog, Sana cateshjana. The number of species north of Mexico 

 is about forty for each of the Anura and Urodela. 



