166 
LAWS OF VAEIATION. 
Chap. V. 
dent, that I was led solely from the occurrence of the 
face-stripes on this hybrid from the ass and hemionus to 
ask Colonel Poole whether such face-stripes ever occur 
in the eminently striped Kattywar breed of horses, and 
was, as we have seen, answered in the afSrmative. 
What now are we to say to these several facts ? We 
see several very distinct species of the horse-genus 
becoming, by simple variation, striped on the legs like 
a zebra, or striped on the shoulders like an ass. In the 
horse we see this tendency strong whenever a dun tint 
appears—a tint which approaches to that of the general 
colouring of the other species of the genus. The 
appearance of the stripes is not accompanied by any 
change of form or by any other new character. We see 
this tendency to become striped most strongly displayed 
in hybrids from between several of the most distinct 
species. Now observe the case of the several breeds of 
pigeons: they are descended from a pigeon (including 
two or three sub-species or geographical races) of a 
bluish colour, with certain bars and other marks; and 
when any breed assumes by simple variation a bluish 
tint, these bars and other marks invariably reappear; 
but without any other change of form or character. 
When the oldest and truest breeds of various colours 
are crossed, we see a strong tendency for the blue tint 
and bars and marks to reappear in the mongrels. I 
have stated that the most probable hypothesis to account 
for the reappearance of very ancient characters, is— 
that there is a tendency in the young of each successive 
generation to produce the long-lost character, and that 
this tendency, from unknown causes, sometimes prevails. 
And we have just seen that in several species of the 
horse-genus the stripes are either plainer or appear 
more commonly in the young than in the old. Call the 
breeds of pigeons, some of which have bred true for 
