II HABITS AND NATURAL HISTORY OF THE FROG 59 



14 per cent of their weight. When placed back in the 

 water again they regained very nearly their previous weight 

 in twenty-four hours. Both the loss and absorption of 

 water were found to take place more rapidly in the summer 

 than in the winter. An experiment by Townson on a species 

 of tree frog showed that a specimen weighing ninety-five 

 grains increased in weight by seventy-six grains after being 

 kept in the water for an hour. 



Shedding of the Skin. — At certain periods the frog casts 

 off its cuticle or outer layer of skin. The part shed consists 

 merely of a very thin transparent membrane only one or 

 two cells thick. This comes off in large patches which may 

 be seen adhering to the animal here and there, the skin 

 covering the toes usually coming off last. The first molt 

 takes place in the spring at about the time of the breeding 

 season. In Rana fusca Fischer-Sigwart found that after the 

 first molt, which occurs from late in February to early in 

 April, a second molt follows in the latter part of May or the 

 first part of June, a third in July, and usually a fourth in 

 August. In colder seasons the period of the molt comes 

 later, and the fourth molt may then not occur. Five molts 

 were not observed even during the warmest summers. Frogs 

 often eat their shed skin after they have rubbed it off with 

 the aid of their feet. The same habit has been observed in 

 toads and in the large salamander, Cryptobranchus. 



Hypnotism. — A frog may be thrown into the so-called 

 hypnotic state in several ways. If it is seized in the hands, 

 laid upon its back, and held a few moments until it has 

 ceased its struggles, it will usually remain motionless for a 

 considerable time, sometimes for hours. The position taken 

 is a variable one. There is a tendency to assume an attitude 

 such as would be produced if the movements of the frog 

 were checked sometime during its efforts to regain an up- 



