PERCHING BIRDS. J 55 



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 



