Chap. XIV. 
EECAPITULATION. 
473 
elusion when we look, for instance, at the logger-headed 
duck, which has wings incapable of flight, in nearly 
the same condition as in the domestic duck; or when 
we look at the burrowing tucutucu, which is occasionally 
blind, and then at certain moles, which are habitually 
blind and have their eyes covered with skin; or when 
we look at the blind animals inhabiting the dark caves 
of America and Europe. In both varieties and species 
correlation of growth seems to have played a most im¬ 
portant part, so that when one part has been modified 
other parts are necessarily modified. In both varieties 
and species reversions to long-lost characters occur. 
How inexplicable on the theory of creation is the occa¬ 
sional appearance of stripes on the shoulder and legs 
of the several species of the horse-genus and in their 
hybrids! How simply is this fact explained if we 
believe that these species have descended from a striped 
progenitor, in the same manner as the several domestic 
breeds of pigeon have descended from the blue and 
barred rock-pigeon! 
On the ordinary view of each species having been 
independently created, why should the specific charac¬ 
ters, or those by which the species of the same genus 
differ from each other, be more variable than the generic 
characters in which they all agree ? Why, for instance, 
should the colour of a flower be more likely to vary in 
any one species of a genus, if the other species, supposed 
to have been created independently, have differently co- 
lom-ed flowers, than if all the species of the genus have the 
same coloured flowers ? If species are only well-marked 
varieties, of which the characters have become in a high 
degree permanent, we can understand this fact; for 
they have already varied since they branched off from a 
common progenitor in certain characters, by which they 
have come to be specifically distinct from each other ; 
