230 OUR SUMMER MIGRANTS. 



It is undeniable that strong impressions upon 

 the sense of sight, affecting the parent during 

 conception or an early stage of pregnancy, may 

 and do influence the formation of the embryo, 

 and it has consequently been asserted that the 

 sight of the eggs lying in the nest has such an 

 influence on the hen Cuckoo, that her egg, which 

 is ready to be laid, assumes the colour and mark- 

 ings of those before her. This is not, however, 

 supported by facts, for the egg of a Cuckoo is 

 frequently found with eggs which do not in the 

 least resemble it (e.g. those of the H edge-Spar- 

 row) ; or with eggs which, from the nature of the 

 nest, could not have been seen by the Cuckoo 

 (as in the case of the Redstart, Wren, or Willow 

 Wren) ; or deposited in a nest before a single 

 egg had been laid therein by the rightful owner. 

 Again, two Cuckoo's eggs of a different colour 

 have been found in the same nest. If both were 

 laid by one bird, we have a proof that the same 

 Cuckoo does not always lay eggs of the same 

 colour ; if laid by different birds, then the Cuckoo 

 is not so impressionable as has been supposed. 



What really takes place, I believe, is this : 



