196 THE ZOOLOGIST. 



deprived of her own mate, had been forced to mate with one of 

 an allied species, seems discredited when we find so many cases 

 of interbreeding as early as March. 



The simplest explanation seems to be that in certain districts 

 the female birds are totally indifferent as to whether they mate 

 with one of their own species or with one of an allied species. 

 Although this seems so opposed to natural direction, I do not 

 think that in practice it would be so difficult. 



We may, then, safely conclude that Blackbirds of both sexes 

 do mate and interbreed with Song- Thrushes, and the eggs are 

 externally influenced, to a certain extent, by the male bird, and 

 that the young resemble the mother bird, with some of their 

 father's characteristics. By far the most usual form of Thrush- 

 interbreeding is the male 1\ merula with the female T. musicus. 

 But it must not be forgotten that in nine cases out of ten the 

 eggs are unfertile, and are never incubated by the female. 



