REPRODUCTION— CONCERNING EGGS 201 



with a large and representative collection of eggs. Firstly, that 

 the colours displayed bore no sort of relation to those of the 

 birds which laid them, and secondly, that there was little about 

 these shells that would enable him to decide the particular 

 species, or even genus, to which such and such an egg belonged, 

 rare cases only excepted. 



At the first blush it may seem curious that since the pigments 

 of egg-shell and of feather are alike derived from the blood, 

 there should be such striking contrast between the colours of a 

 bird and the eggs which it lays. This contrast is marked in- 

 deed in such species, for example, as the Hedge-sparrow and the 

 Thrush, whose eggs are blue, yet in the matter of plumage they 

 are the most sober-coloured of birds ; while the gorgeously clad 

 Kingfishers and the Bee-eaters lay milk-white eggs. But the 

 explanation of these things is not far to seek. In the first place, 

 the colours of feathers are often due, not to pigment, but to 

 structure (p. 284). This is never the case with eggs. The wonder- 

 ful iridescent blue of the Kingfisher is a case in point, for the 

 blue colours of the feathers are never due to pigment. In the 

 second place, the coloration of the shell is, on the whole, as 

 much governed by natural selection as are the colours of the 

 feathers of the bird which laid them. To this point we shall 

 return presently. For the moment we must pass to the question 

 of markings of the shell, though there is unfortunately at present 

 little enough that can be said on this head. We have indicated 

 already the process by which these markings are made, and all 

 that can further be said on the subject may now be briefly sum- 

 marised. They range then from minute frecklings, such as are 

 met with in some Game-birds, through sharply defined dots, to 

 blotches and smears, and irregular lines and streaks which sug-, 

 gest hieroglyphics of some sort, as in the eggs of Burftings and 

 the Jacanas among the Plovers ; while many eggs are what is 

 called " double-spotted " on account of the fact that many of 

 these spots are but faintly indicated, 'and evidently deposited in 

 a deeper layer of the shell. In s(Jtne eggs, as in those of certain 

 Petrels, the pigment is almost, and sometimes entirely, confined 

 to a zone around the larger end. But perhaps the most striking 

 fact about this coloration is the lack of uniformity which pre- 

 vails among even closely allied species, species which in plumage 

 bear an exceedingly close resemblance, while birds in no way 



