336 GENERAL ZOOLOGY 



If the adult condition has not been reached, the tadpole 

 continues its growth the following summer. The hind legs 

 appear (Fig. 167, 7, 8), and grow to be about an inch long, 

 when the fore legs suddenly appear (Fig. 167, 9, 10). The 

 front legs are really formed as early as the hind legs, but they 

 are kept beneath the skin for a while. The broad and com- 

 pressed tail, which forms the tadpole's chief organ of loco- 

 motion, is gradually absorbed, and the young frog finally hops 

 out on land with only a stump of a tail remaining (Fig. 167, 11). 

 By the time these changes have taken place externally, im- 

 portant changes have gone on inside : the gills have been 

 replaced by lungs ; one of the chambers of the heart has been 

 divided; the intestine has become shorter, fitting the frog 

 better for an animal-diet; and the horny jaws have given 

 place to a wide mouth with teeth. This metamorphosis is 

 retarded by cold, and accelerated by rest and freedom from 

 disturbance of the water. The frog (Fig. 167, 12) grows for 

 several years without further metamorphosis, except the 

 gradual disappearance of the stump of the tail. Through- 

 out life the outer skin is cast periodically in a single piece 

 and immediately devoured. 



Relation to Environment. The dark-green and brown colors 

 of the upper surface afford considerable protection among the 

 water-plants and along the muddy or grassy margins of ponds 

 and streams, and the white under surface may be similarly 

 useful in the water. 



The green frog is a voracious feeder, and varies its diet 

 with almost every kind of small creature which comes its 

 way, not hesitating in the least to devour smaller individuals 

 of its own kind. Usually only moving objects are seized, and 

 it has been said that the frog may starve to death in the 

 midst of an abundance of food if there is no movement to 

 attract its attention. The eyes are situated high on the top of 

 the head, where they maintain a wide survey. Every boy in 



