with a different colour from the rest are very inconstant, and during
certain years some, or even all the flowers, become uniformly coloured; and
it has been observed with several varieties,[831] that when this happens
the petals grow much elongated and lose their proper shape. This, however,
may be due to reversion, both in colour and form, to the aboriginal
species.

* * * * *

In this discussion on correlation, we have hitherto treated of cases in
which we can partly understand the bond of connexion; but I will now give
cases in which we cannot even conjecture, or can only very obscurely see,
what is the nature of the bond. Isidore Geoffroy St. Hilaire, in his work
on Monstrosities, insists,[832] "que certaines anomalies coexistent
rarement entr'elles, d'autres frequemment, d'autres enfin presque
constamment, malgre la difference tres-grande de leur nature, et
quoiqu'elles puissent paraitre _completement independantes_ les unes des
autres." We see something analogous in certain diseases: thus I hear from
Mr. Paget that in a rare affection of the {332} renal capsules (of which
the functions are unknown), the skin becomes bronzed; and in hereditary
syphilis, both the milk and the second teeth assume a peculiar and
characteristic form. Professor Rolleston, also, informs me that the incisor
teeth are sometimes furnished with a vascular rim in correlation with
intra-pulmonary deposition of tubercles. In other cases of phthisis and of
cyanosis the nails and finger-ends become clubbed like acorns. I believe
that no explanation has been offered of these and of many other cases of
correlated disease.

What can be more curious and less intelligible than the fact previously
given, on the authority of Mr. Tegetmeier, that young pigeons of all
breeds, which when mature have white, yellow, silver-blue, or dun-coloured
plumage, come out of the egg almost naked; whereas pigeons of other colours
when first born are clothed with plenty of down? White Pea-fowls, as has
been observed both in England and France,[833] and as I have myself seen,
are inferior in size to the common coloured kind; and this cannot be
accounted for by the belief that albinism is always accompanied by
constitutional weakness; for white or albino moles are generally larger
than the common kind.

To turn to more important characters: the niata cattle of the Pampas are
remarkable from their short foreheads, upturned muzzles, and c