CHAPTEK I 

 THE BREEDING SEASON 



" To everything there is a season, and a time to every purpose under the 

 heaven." Ecclesiastes iii. 1. 



" IT is well known that almost all animals, except man, have a 

 stated season for the propagation of their species. Thus the female 

 cat. receives the male in September, January, and May. The she- 

 wolf and fox in January ; the doe in September and October. The 

 spring and summer are the seasons appointed for the amours of 

 birds, and many species of fishes. The immense tribe of insects 

 have likewise a determinate time for perpetuating their kind ; this 

 is the fine part of the year, and particularly in autumn and spring. 

 The last-mentioned class of beings is subject to a variation that is 

 not observed in the others. Unusual warmth or cold does not retard 

 or forward the conjunction of birds or quadrupeds; but a late spring 

 delays the amours of insects, and an early one forwards them. Thus 

 it is observed that, in the same country, the insects on the mountains 

 are later than in the plains." 



The foregoing quotation from Spallanzani's "Dissertations," 1 

 although not strictly accurate in all its statements, contains a 

 clear recognition of two fundamental facts which indeed have 

 been realised from the earliest times; first, that the periods of 

 reproductive activity among the great majority of animals (not to 

 mention plants) occur rhythmically, the rhythm having a close 

 connection with the changes of the seasons ; and secondly, that the 

 reproductive rhythm is liable, to a greater or less extent, to be 

 disturbed or altered by climatic or other environmental influences. 

 And while there may be a basis of truth for the statement that the 

 periodicity of the breeding season in the higher animals is less liable 

 to modification than is the case with certain of the lower forms of 

 life, there is abundant evidence that among the former no less 

 than among insects the sexual functions are affected by external 

 conditions and food supply. 



Darwin remarks that any sort of change in the habits of life of 



1 Spallanzani, Dissertations relative to the Natural History of Animals and 

 Vegetables. Translated from the Italian, vol. ii., London, 1784. 



