CLAIMS OF OOLOGY TO BE AN EXACT SCIENCE. 241 
a different species is recognisable from one laid by the same 
bird when paired with a male of her own.” And Mr Howard 
Saunders tells us that nests of the Orphean Warbler, obtained 
by him near Malaga, sometimes contained one or even two 
eggs which were much larger than the normal eggs of that 
bird, though identical in colour. He submitted these large 
eggs to Prof. Sorby, who by microscopic investigation of the 
texture discovered that they belonged to Cuculus canorus. 
But our knowledge of the causes which affect the texture of 
birds’ eggs is extremely imperfect. All that we do know is 
that the texture is rough or smooth according to the number, 
position, and size of the pores. But this goes only a small 
way to explain the marvellous gloss of the egg of the Tina- 
mou, the calcareous coating of that of the Guira Cuckoo, or 
why the egg of a duck of the genus Dendrocygna should be 
as smooth as that of one of the genus Erismatura is rough. 
6. CoLourR. 
The widely varied coloration of eggs is the most complex, 
as it is the most interesting, of all the problems which the 
oologist has to solve. No one who looks at a collection of 
birds’ eggs can fail to be struck by the remarkable beauty 
of many of the specimens. For, as Prof. Newton has said, 
“hardly a shade known to the colourist is not exhibited by 
one or more, and some of these tints have their beauty 
enhanced by the glossy surface on which they are displayed, 
by their harmonious blending, or by the pleasing contrasts 
of the pigments which form markings as often of the most 
irregular as of regular shape.” Now, what is the reason for 
all this varied and beautiful colouring? For, believing as we 
all, of course, do, that birds have been evolved from a lizard- 
like ancestor, and knowing that the eggs of all reptiles are 
white, we are pretty safe in assuming that the eggs of all 
birds, too, were originally of an uniform white colour. The 
author of the standard work on British Oology says the 
purpose served by the beautiful and varied colours lavished 
so abundantly on the eggs of various species of birds is to 
minister delight unto man and to beautify the earth. He 
