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 te 
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 
