The Descent of Man

can forms which until lately were named as
distinct species, are now considered to be local
races.) Variations may be divided into two classes;
those which appear to our ignorance to
arise spontaneously, and those which are directly
related to the surrounding conditions, so
that all or nearly all the individuals of the same
species are similarly modified. Cases of the
latter kind have recently been observed with
care by Mr. J.A. Allen (34. 'Mammals and Birds
of East Florida,' also an 'Ornithological Reconnaissance
of Kansas,' etc. Notwithstanding the
influence of climate on the colours of birds, it is
difficult to account for the dull or dark tints of
almost all the species inhabiting certain countries,
for instance, the Galapagos Islands under
the equator, the wide temperate plains of Patagonia,
and, as it appears, Egypt (see Mr. Hartshorne
in the 'American Naturalist,' 1873, p.
747). These countries are open, and afford little
shelter to birds; but it seems doubtful whether
the absence of brightly coloured species can be