PERCHING BIRDS. 155 
point on which the Doctor lays stress is what he calls 
the grain of the shell. I have been unable to detect 
this. I have examined under a low magnifying power 
the eggs of the cuckoo, as well as those of the hedge- 
sparrow, the meadow pipit, the pied wagtail, and others, 
and can see no difference in this respect. 
I am at a loss to see what purpose can be served by 
such an alleged resemblance. The German professor 
says it is to prevent them being detected by the owners 
of the nest, and ejected or destroyed, and thus the con- 
tinuance of the species is insured. Is this necessary ? 
If so, the American Cow Bird (Icterus pecoris), which 
deposits its eggs in the same manner as the cuckoo, 
should possess this advantage for the same ends: and 
yet Wilson says of it, “these odd-looking eggs were all 
of the same colour, and marked nearly in the same 
manner, in whatever nest they lay, though frequently the 
eggs beside them were of a quite different tint.” No 
variation is discoverable here, and yet the species does 
not fail ; but, reasoning from analogy, if it is necessary in 
one case, it is in the other. 
There are two conclusions to which we are shut up by 
this theory. First, every cuckoo must possess the power 
of colouring her eggs at will; or, secondly, there are 
thirty-seven kinds, each kind laying different eggs, but 
which are constant in their colour and markings. 
With regard to the first, I believe a cuckoo does not 
seek a nest until her egg is ready for extrusion, and con- 
sequently mature, having received its colour and mark- 
ings from the glands in the lower portion of the oviduct, 
and this is confirmed by the opinion held by many 
naturalists, that she possesses the power of retaining her 
egg after it is ready, until she can find a nest for its 
