242 MR J. B. DOBBIE ON 
then, in support of his argument, goes on to say that the 
eggs of all birds which build in holes are white because 
there is, in such situations, no necessity for glowing colours; 
but this is not literally true, because the eggs of many birds 
which build in holes are not white, but are richly coloured 
—for instance, those of the Kestrels, Tree-Sparrow, and Nut- 
hatch; and we may be tempted to ask why the egg of the 
Falcon should not be white instead of that blood-red tint 
which makes it so conspicuously beautiful; because if we 
apply the foregoing argument, there is as little need for 
glowing colours in the inaccessible precipice as there is for 
them in holes in trees. According to a well-known German 
naturalist, the coloration of birds’ eggs is for protective 
purposes. And there can be no doubt that the majority of 
eggs deposited on the bare ground afford strong proof in 
favour of his hypothesis. It is, for example, impossible to 
conceive protective coloration more perfect than that exhibited 
by the eggs of the Ringed Plover or Lesser Tern, for so closely 
do they resemble the shingle on which they are laid that 
they almost defy discovery. Yet it is obvious that in the 
vast majority of cases the resemblance of the eggs to their 
surroundings would, for protective purposes, be superfluous, 
for if the nests were discovered, what further security would 
be afforded by the eggs? Then we have the theory of Dr 
M‘Aldowie, that the use of colour is primarily to protect the 
egg, or rather the embryo within it, from the solar rays. 
But this hypothesis, too, clever as it is, utterly fails in many 
cases to solve the difficulty. If time had permitted, an 
extensive list of eggs could have been prepared which are of 
a pure white colour even when exposed to the full force of 
the sun’s rays, and of brightly coloured eggs placed where 
no sunlight can ever penetrate. Widely different is the 
verdict pronounced by recent research. “Whence, then,” 
says Wickmann, “ proceed all these differences? Why are 
different pigments secreted in the organisms of different birds ? 
My answer is: The only source of all egg-colouring is the 
blood.” The eggs of the different species of a well-defined 
genus,such as Hypolais and Oriolus, bear a striking resemblance 
to each other, though here I may say that the selection of 
Emberiza as a typical case by the South Kensington authorities 
