188 EGGS 
think that Oorhodeine is in some way or other closely related to 
Cruentine, being probably derived from the red colouring-matter 
of the blood by some unknown process of secretion, and likewise that 
there is some chemical relation between the Oocyans and the bile. 
It was remarked by Hewitson in 1838 (Brit. Oology, Introd. p. 8), 
and perhaps he was not the first to make the observation, that 
the eggs of many if not of most birds which breed in holes, or 
even in covered nests, are of an uniform white ; but the number of 
exceptions is so great, that no general rule can be laid down to this 
effect. Conversely, the number of birds which lay purely white 
eggs in open nests—the multitudinous species of PIGEON being 
notorious instances of the fact!—is also large, and in some respects 
quite independent of their taxonomic relations, as, for example, the 
Little BrrreRN among the Ardeidx, the Virginian QUAIL among 
the so-called “ Odontophorinx,” and again among the Gallinw even 
the Common Fowl, though some of its breeds, perhaps acted upon by 
what is known as “reversion,” lay coloured eggs. The eggs of OWLS 
are always white, whether the species be one that breeds in holes, 
on the bare ground, or in an open nest ina tree. The egg of the 
Gos-HAWK is white, but that of its small relative the Sparrow- 
HAWK is always blotched, and sometimes richly, with pigment, the 
nest of both being built precisely in the same kind of position,— 
but it would be almost endless to cite similar cases. To account 
for some, at least, of these anomalies, an ingenious hypothesis has 
been set forth by Dr. M‘Aldowie,? starting on the assumption “ that 
the pigmentary coat on birds’ eggs came into existence at a very 
early period in their life-history, and existed in the eggs of the 
progenitors of all the extant species.” It is further taken as proved 
that the pigments being “unstable and variable” makes “the pro- 
cess of change and decolorization a simple one; and that its 
primary use is for protection from the solar rays, but that it 
afterwards becomes modified for concealment.” Finally, it is main- 
tained “that eggs acquire a highly developed pigmentary layer, 
or lose their pigment entirely, according to whether they are ex- 
posed to the full glare of the sun or laid in situations inaccessible 
to its rays, and that the intermediate degrees of coloration are in 
direct ratio to the amount of light to which the eggs are exposed.® 
1 Of course, Columba livia, and its allies C. schimpert and C. intermedia, 
usually breed in caves, and C. wnas generally though not always places its nest 
under cover, but these seem to be the only exceptions in a Family comprising 
some 350 species. 
” Observations on the Development and the Decay of the Pigment Layer in 
Birds’ Eggs, Journ. Anat. and Physiol. xx. (1886), pp. 225-237. 
3 It is to be observed that the author bases his hypothesis on a study of the 
eggs of British birds only. Considering that in most respects the most instruc- 
tive forms of the Class do not belong to our own limited fauna, allowance 
must be made for the imperfect information whence his results are drawn. 
