160 
LAWS OF YAKIATION. 
Chap. V. 
rump, a bar at the end of the tail, with the outer 
feathers externally edged near their bases with white. 
As all these marks are characteristic of the parent rock- 
pigeon, I presume that no one will doubt that this is a 
case of reversion, and not of a new yet analogous varia' 
tion appearing in the several breeds. We may I think 
confidently come to this conclusion, because, as we have 
seen, these coloured marks are eminently liable to ap¬ 
pear in the crossed offspring of two distinct and differ¬ 
ently coloured breeds; and in this case there is nothing 
in the external conditions of life to cause the reappear¬ 
ance of the slaty-blue, with the several marks, beyond 
the influence of the mere act of crossing on the laws of 
inheritance. 
No doubt it is a very surprising fact that characters 
should reappear after having been lost for many, perhaps 
for hundreds of generations. But when a breed has 
been crossed only once by some other breed, the offspring 
occasionally show a tendency to revert in character to 
the foreign breed for many generations—some say, for 
a dozen or even a score of generations. After twelve 
generations, the proportion of blood, to use a common 
expression, of any one ancestor, is only 1 in 2048; and 
yet, as we see, it is generally believed that a tendency 
to reversion is retained by this very small proportion of 
foreign blood. In a breed which has not been crossed, 
but in which hoth parents have lost some character 
which their progenitor possessed, the tendency, whether 
strong or weak, to reproduce the lost character might 
be, as was formerly remarked, for all that we can see 
to the contrary, transmitted for almost any number of 
generations. When a character which has been lost in 
a breed, reappears after a great number of generations, 
the most probable hypothesis is, not that the offspring sud¬ 
denly takes after an ancestor some hundred generations 
