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, 
ete., 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, Rana cateshyana. The number of species north of Mexico 
is about forty for each of the Anura and Urodela, 
