The Zoologist — October, 1873. 3725 



that it would have been almost impossible to distinguish between 

 them."* It is true this may be mere mimicry, or the result of 

 imitation ; but it must be remembered that in calling for food, the 

 young cuckoo can only imitate the note of its foster-parents, its 

 fosiex -brethren having perished on its account in their infancy. 

 Here then we have the young cuckoo in one important respect 

 partaking of the nature of its foster-parents. I do not, however, 

 wish to push this point too far, or to lay greater stress upon it than 

 it deserves. Let it be taken for what it is worth, though I think it 

 deserves consideration in connection with the subject before us. 



And now, in support of my fancy, I first unhesitatingly assert 

 that the cuckoo, about to lay her egg, has no more notion of its 

 colour than any other bird has. The will of the parent has nothing 

 whatever to do with it. I am too ignorant of the process by which 

 the pigment or colouring matter is diffused over the egg, or of the 

 exact moment when it receives that pigment before leaving the 

 oviduct, to be able to show by conclusive reasoning that birds, of 

 whatever species, are wholly passive and unconscious, while the 

 colouring of their eggs is going on ; but I venture to assert, without 

 much fear of opposition, that such is the case with all birds, and 

 with the cuckoo not less than with other species. 



What it is that influences the colouring matter, and produces 

 a blue egg for one species, a brown egg for another, and a reddish 

 egg for a third, I can no more describe than I can account for the 

 varying colours in plumage in the respective species of birds. 

 Whether the colouring process in regard to the egg is influenced in 

 any degree by the kinds of food the bird eats, I do not know; 

 though that food has an effect on the colour of the plumage of 

 birds I do know ; of this the familiar case of the bullfinch 

 becoming black if fed on hemp-seed, is a well-known and sufficient 

 example. 



Next, I submit that in all probability the young of the several 

 species of even our insect-eating warblers are not fed on precisely 

 the same diet. This in many cases is obvious j because whereas 

 one species procures its insect-food near the banks of streams or 

 ponds, another in our meadows and gardens, and another in the 

 hedgerows and ditches, these must undoubtedly feed their young 

 on the insects which abound in the districts they severally frequent. 

 Then I think it is not improbable that the same rule holds good in 



* • Natural History of Ireland,' vol. i. p. 300. 

 SECOND SERIES — VOL. VIII. 8 D 



