402 



COLLEGE ZOOLOGY 



Figure 271. Necturus, commonly called mud 

 puppy. An aquatic species about 1^/2 feet long. 

 (New York Zoological Society Photo.) 



americanus) (Fig. 272), possesses a rough, 

 warty skin, but it does not cause appearance 

 of warts upon the hands of those who han- 

 dle it, as is often supposed. Toads secrete a 

 milky poisonous fluid by means of glands in 

 the skin, which protects them from many 

 animals that would otherwise be important 

 enemies. During the day they remain con- 

 cealed in some dark damp place, but at night 

 they hop about, feeding upon worms, snails. 



Figure 272. The common American toad. Note 

 warty skin, bright markings, and jewel-like eye. Nat- 

 ural size 3V2 inches long. (Courtesy of the American 

 Museum of Natural History.) 



and especially insects, which they capture 

 with their sticky tongues as frogs do. 



Tree frogs 



Tree frogs are usually jirboreal amphib- 

 ians with adhesive disks en their toes and 

 fingers that usually enable them to climb 

 trees. They are provided with large vocal 

 sacs and have a correspondingly loud voice; 

 see headpiece at beginning of this chapter 

 for illustration of vocal sacs distended with 

 air. Of the more than 180 species, 21 occur 

 in the United States and about 130 in Cen- 

 tral and South America. The common tree 

 frog, Hyla versicolor (Fig. 267), is about two 

 inches long. Other common tree frogs are 

 the spring peeper, Hyla crucifer, and the 

 cricket frog, Acris gryllus. 



True frogs 



The family Ranidae contains the true 

 frogs. These occur in all parts of the globe 

 except Australia, New Zealand, and southern 

 South America. Only one genus, Rana, and 

 about 16 species live in the United States. 

 Of these, the leopard frog (Fig. 217) is the 

 most common. The bullfrog Rana cates- 

 beiana (Fig. 267) is the largest of the family 

 in this country, often reaching a body length 

 of 6 or 8 inches. Bullfrogs usually remain in 

 or near water. They possess a deep bass voice 

 like that of a bull. The tadpoles do not be- 

 come frogs the first year, as do those of the 

 leopard frog, but transform during the sec- 

 ond or even the third year. Other true frogs 

 include the green frog Rana clamitans, the 

 eastern wood frog Rana sylvatica, and the 

 pickerel frog Rana palustris. 



RELATIONS OF 

 AMPHIBIA TO MAN 



Amphibians are virtually all beneficial to 

 man. Many are so rare as to be of little value, 

 but the frogs and toads are of considerable 

 importance. Frogs have been and are now 



