164 THE STORY OF BIRD-LIFE. 



semblance to that of the species selected to act 

 the part of wet-nurse. He claims to be able to 

 recognise every egg laid by any particular bird, 

 not only during that season but during every 

 season so long as she continues to return each 

 year to the same district to lay in. This he 

 seems able to do from the fact that each cuckoo 

 has a more or less distinctive colouration for its 

 shell, which makes it perfectly easy to identify ; 

 it is a sort of visiting-card. Thus, if a bird lays 

 in a red-backed shrike's nest its egg will resemble 

 that of this species ; if in a pipit's, then of this, 

 and so on. If the red-backed shrike be the victim 

 selected then she will go the round of all the 

 red-backed shrikes' nests in the neighbourhood 

 laying an egg in each, till all her stock of eggs 

 for that year is exhausted. Only, it appears, 

 when there are no more nests of the required 

 species to be found will she drop her egg into 

 that of some other. The resemblance between 

 the egg of the cuckoo and that of the foster- 

 parent selected is attributed to the influence 

 of the food during the nestling period of each 

 particular cuckoo. The colouring matter of say 

 the red-backed shrike's egg is more or less deter- 

 mined by the nature of the parent's food. The 

 nestling cuckoo, being fed like a nestling shrike, 

 the influence of this feeding is transmitted through 

 the germplasm to its offspring. Shrike and cuckoo, 

 in this respect, are influenced alike. The sound- 

 ness of this conclusion has yet to be tested. 



Having been reared by shrikes, it seems that 

 it cherishes a certain sort of affection for them, and 

 on arriving at maturity entrusts its offspring to 



