THE FROG'S YEAR 49 



break the silence of Nature was that of Amphibians. 

 The primary function of the voice was probably as a 

 sex call, and that is its almost exclusive use in frogs. 

 After the breeding season is over, the male grass- 

 frog is almost as taciturn as the female. It is 

 surely suggestive to think of the secondary employ- 

 ment of the voice in higher vertebrates in protecting 

 and fostering the young, in expressing pain and 

 pleasure, in communicating social news. As Pro- 

 fessor Holmes notes in his interesting Studies in 

 Animal Behaviour (1916) : "The evolution of the 

 voice in vertebrates doubtless influenced in a marked 

 degree the evolution of the sense of hearing. It is 

 not improbable, therefore, that the evolution of 

 the voice, with all its tremendous consequences in 

 regard to the evolution of mind, is an outgrowth of 

 the differentiation of sex." 



In this connection it is worth noticing that 

 although frogs have poor brains, and are of course 

 limited by their "cold-bloodedness," which makes 

 their changeful body-temperature approximate to 

 that of their immediate surroundings, they are pro* 

 foundly affected at the sex season. The pairing 

 and egg-laying may occur while there are still 

 lumps of ice in the water, and before the creatures 

 have broken their fast! The male has not only 

 his resonating sacs, but a curiously swollen and 

 hardened tetrapartite pad on his first finger, which 

 he uses in violently embracing his mate. His 

 whole skin changes considerably, and often shows 

 a beautiful bluish sheen. The character of the 



