8510 The Zoologist— May, 1873. 



particular golden eagle has gone on season after season laying eggs 

 that could be at once distinguished by a practised eye from the 

 eggs of almost any other golden eagle ; and I know of one case 

 in which the presumed daughter of a particular golden eagle, re- 

 markable for having produced eggs of very great beauty, has in 

 two successive years laid eggs which unmistakably resembled 

 those of her reputed mother in the brilliant character of their 

 colouring. 



Hence I am not afraid of hazarding the supposition, that the 

 habit of laying a particular style of egg is likely to become here- 

 ditary in the cuckow ; just as I have previously maintained that 

 the habit of depositing that egg in the nest of a particular kind of 

 bird is also likely to become hereditary. 



Now it will be seen that it requires but an application to this 

 case of the principle of "Natural Selection" or "Survival of 

 the Fittest" to show that if my argument be sound, nothing can 

 be more likely than that, in the course of time, that principle would 

 operate so as to produce the facts asserted by the anonymous 

 Sologuot of a hundred years ago, and by Dr. Baldamus and others 

 since. The particular gens of cuckow which inherited and trans- 

 mitted the habit of laying in the nest of any particular species of 

 bird, eggs having more or less resemblance to the eggs of that 

 species, would prosper most in those members of the gens where 

 the likeness was strongest, and the other members would {ccstei-is 

 paribus) in time be eliuiinated. It is not to be supposed that all 

 species, or even all individuals of a species, are duped with equal 

 ease. The operation of this kind of " Natural Selection" would 

 be most marked in those cases where the species are not easily 

 duped, that is, in those cases which occur the least frequently. 

 Here it is that we find it, for it has been shown that eggs of 

 the cuckow, deposited in the nests of the red-backed shrike, of the 

 buntiug-laik, and of that bird which for some reason best known to 

 the donor bears the English name of " Melodious Willow-warbler," 

 approximate in their colouring to the eggs of those species — 

 species in whose nests the cuckow rarely (in comparison with 

 others) deposits her eggs. Of species which would appear to be 

 more easily duped, or duped in some other manner — the species in 

 whose nests cuckow's eggs are more commonly found, I may 



have something to say in another paper. 



Alfred Newton. 



