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NESTS AND EGGS. 
the blood in the ovary, mixing with the calcareous salts of 
which the shell is composed. “ Jt results not only from an 
excretion of the calcareous salt,” he says, speaking of the 
shell ; “ for the blood of the oviduct, being in a sort of inflamma- 
tory state, mixes itself with these salts, forming certain pro- 
ducts, to which may be attributed the divers colours of the eggs 
of birds. All these varied tints are the result of the decomposi- 
tion of the blood.” It is possible that the colour of eggs may 
be due to some such cause, but the subject is open to doubt; 
for if the source of the colour and spots is in the blood mixing in 
the uterine vessels with the salts of the shell, it is difficult to 
conceive why all eggs are not spotted, and why those that are 
spotted vary in tint. Besides, the colour, whatever it may be, 
is only external, forming a thin coating only; whereas, if it 
had been produced by a mixture of decomposed blood and the 
component parts of the shell, the whole shell would partake of 
the prevailing colour. In the meanwhile, the question is still 
one of doubt; a doubt, perhaps, which chemical analysis would 
easily solve were the question one of any moment. 
It has been observed that eggs laid im cavities or dark 
places, where light is altogether absent, are generally white 
and free from spots; such are those of the several species of 
owls, the kingfisher, the wood-pigeon, which builds its nest 
in the depths of some deeply-shaded wood, and some others 
which might be named. Those, on the contrary, which are 
laid exposed to the light, are generally more or less richly 
coloured. Might we not conclude from these facts that light 
has a marked action upon the colouring of the eggs, as it has 
on other productions of nature? The flower which blooms in 
shade and obscurity, is it not pale and shrivelled, like everything 
denied the vivifying rays of the sun? The birds themselves 
being a proof of this simple fact; for those of the most 
brilliant and varied plumage are the inhabitants of imter- 
tropical countries. 
Now, as eggs are generally spotted, and as the notion pre- 
vails that the stains increase not in size but in intensity, in 
proportion as the embryo developes itself, some ornithologists 
have thought they could trace a resemblance between the spots 
of the eggs, the nest of the birds, and their plumage. All 
application, however, of a rule, which would deduce the 
colour of a bird from the colour of the eggs, appears to be 
unsupported by any number of facts; on the contrary, all the 
facts are opposed to it. Thus, the golden Pa a bird so 
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