II HABITS AND NATURAL HISTORY OF THE FROG 53 



bered over her back, when the clasping instinct suddenly took 

 possession of him, and he remained clasping her body. 

 Later in the season this clasping instinct disappears. 



Hibernation.- -In the late fall frogs betake themselves 

 to water and bury themselves in the mud out of reach of 

 frost. Here they lie in a dormant condition until the next 

 spring. The general vital activities of the animal run down 

 so low that little expenditure of energy is required to maintain 

 life. There is need, therefore, for only a small amount of 

 oxygen, and skin respiration then suffices. During the 

 whole winter the frog does not breathe air with the lungs. 

 The temperature of the body sinks until it is only a few 

 degrees above that of the surrounding medium. As the 

 frog takes no food during this time, it must keep up its vital 

 activity at the expense of material stored in its tissues. Its 

 temperature, even if only a little above that of its surround- 

 ings, requires the use of a certain amount of combustible 

 material for its support. During the summer the frog feeds 

 voraciously, and when cold weather ensues, its system is 

 stored with a rich supply of food material which is gradually 

 expended through the winter months. This food must keep 

 the heart beating and support the various activities of the 

 physiological machinery of the body. And in addition to 

 supplying energy for this purpose, it must afford the sub- 

 stance for the growth of the sexual products, which increase 

 during the winter at the expense of the other parts of the 

 organism. 



Life in Summer. -- After the eggs are laid in the early 

 spring, the frog leads an active predatory and solitary life. 

 After its long winter sleep and the expenditure of substance 

 and energy during the breeding season which closely follows 

 the awakening in the spring, the frog is naturally in great 

 need of food, and it becomes a very voracious feeder. Dur- 



