COLOUR IN BIRDS’ EGGS. 251 
immediately? We know that a Bullfinch fed on hemp-seed and 
a Canary on Cayenne pepper become black and orange 
respectively. Mr. Wallace, too, has given (I think in ‘ Tropical 
Nature’) a remarkable instance of change of colour, caused by 
food, in a Brazilian parrot.* Not much is known on the subject, 
still I cannot help thinking that in this case of the Cuckoo we 
should soon have well-marked varieties ; unless we are to believe 
that the impossibility of always finding the desired nest, and the 
mating with birds brought up by a different species, would 
counteract this tendency. 
Nor do I think that Mr. Lucas helps us much. According to 
his view the Cuckoo determines beforehand what nest to lay its 
egg in, looks at the eggs therein contained, and has such a vivid 
impression of their appearance during the period of formation of 
the shell, that the egg which she eventually lays resembles those 
in the nest. 
The Cuckoo has so often been discovered carrying its egg in 
its bill, apparently searching for a nest in which to deposit it, 
that evidence would first be required to show that the bird had 
previously examined the eggs of the nest in which she intended 
to lay her own. 
Prof. Newton, in Yarrell’s ‘ British Birds’ (ed. 4., vol. ii., 
p. 408), says that the supposition that the colour of the egg can 
“in any mysterious way be affected by the action of external 
objects on her perceptive faculties,” is “wholly unreasonable.” 
And certainly Mr. Lucas’s view does seem to be somewhat far- 
fetched. 
If we take the latest List of British Birds, and look through 
it from the Missel Thrush onwards, besides the two obvious 
generalisations with regard to the eggs and nests (viz., that birds 
which build in holes are brightly coloured, and that eggs laid in 
holes are colourless), it is remarkable that the brightly coloured 
eggs are laid by birds at the top of the list; the plain coloured 
eggs by those at the end of the list. The brightness of the 
colour of the egg may be roughly taken to indicate the develop- 
ment of the esthetic faculties of the bird, as shown by singing 
and the nest-building instinct. 


* This statement as to Chrysotis festiva is said to need corroboration. 
Vide Semper’s ‘ Animal Life,’ p. 67. 
