458 The Bird 



hatched and reared by foster-parents. Such an unusual, 

 almost unique habit has brought about a considerable 

 modification of the eggs. Anything which would tend to 

 deceive the greatest number of intended victims would, 

 of course, greatly redound to the advantage of parasitical 

 birds. 



The remarkable similarity of the English Cuckoo's egg 

 to those in the nest in which it is laid has been explained 

 as due to each individual bird being accustomed to lay its 

 egg in the nest of the same species favoured by its parents 

 and its more distant ancestors; its eggs in course of time, by 

 natural selection, thus coming to resemble the eggs of that 

 particular species. Other adaptations are the extremely 

 small size of the egg in comparison with the parent bird, 

 and also the unusual strength and weight of the shell. 

 This last is doubtless of great value; for, strange as it 

 may seem, the bird first deposits its egg upon the ground 

 and then picks it up in its beak and places it in the nest 

 selected. Thus a strong shell is a very necessary require- 

 ment. 



The colours of eggs have been carefully examined with 

 the spectroscope and are found to consist, chemically, of 

 seven pigments: a brownish red, two delicate blues, two 

 clear j^ellows, a peculiar brown hue, while the seventh is a 

 rather indefinite shade, known as lichenixanthine — most 

 interesting of all as being identical with a colour substance 

 common in plants and especially in lichens and fungi. 

 These substances somewhat resemble those found in the 

 blood and the bile. They are deposited on the shell while 

 the egg is passing down the oviduct, and it is to the circular 



