132 JOTTINGS ABOUT BIRDS. 



the fact of the young bird's tendency to seek the 

 companionship, the haunts, and the nests of such 

 species as brought it to maturity, or befriended it 

 in the time of its desertion and helplessness, rather 

 than to the chance laying of an egg in some alien 

 nest by an adult bird. The great variety in the 

 colour of the eggs of the European Cuckoo, for 

 instance, appears to me to confirm this view of the 

 question in no uncertain way. The colour of all 

 birds' eggs is hereditary, not only the general 

 colouration, but to a great extent the details and 

 individual peculiarities. The eggs of the Cuckoo 

 vary considerably so far as concerns the species, 

 but only slightly, so far as we can ascertain, as 

 concerns individual peculiarities ; and to a re- 

 markable extent these various types of eggs are 

 dropped into nests of such species whose eggs 

 most nearly resemble them in colour. Now the 

 tendency of the young Cuckoo being to make use 

 of the nest of the species in which it was itself 

 reared, we can understand how certain types of eggs 

 were gradually evolved and preserved in this species, 

 and how those certain types have become more or 

 less constantly deposited in nests containing eggs 

 resembling them in colour. This is further con- 

 firmed by the fact, that in certain districts there is 



