THE GREEN FROG 341 



of the chambers of the heart has been divided ; the intes- 

 tine 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 disturb- 

 ance of the water. The frog grows for several years without 

 further metamorphosis, except the gradual disappearance 

 of the stump of the tail. Throughout life the outer skin is 

 cast periodically in a single piece and immediately devoured. 



Tadpoles fed on thyroid gland transform to frogs long 

 before their natural time, and tadpoles from which the 

 thyroid is removed by an operation never undergo meta- 

 morphosis. 



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 that comes its 

 way, not hesitating in the least to devour smaller individ- 

 uals 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 the country knows of the difficulty of approaching these 

 alert creatures, and he knows, too, how to capture them 

 by dangling a hook with a piece of red flannel in front of 

 them. Even if well fed the frog seems to find the moving 

 object irresistible, and seizes it with wide-open mouth. 

 The tongue is covered with a sticky substance and can be 

 swiftly extended with unerring aim to a distance of several 

 inches. 



