266 
HYBRIDISM. 
Chap. VIII. 
are produced by the unnatural crossing of two species, 
the reproductive system, independently of the general 
state of health, is affected by sterility in a very similar 
manner. In the one case, the conditions of life have 
been disturbed, though often in so slight a degree as to 
be inappreciable by us; in the other case, or that of 
hybrids, the external conditions have remained the same, 
but the organisation has been disturbed by two different 
structures and constitutions having been blended into 
one. For it is scarcely possible that two organisations 
should be compounded into one, without some disturb-, 
ance occurring in the development, or periodical action, 
or mutual relation of the different parts and organs one 
to another, or to the conditions of hfe. When hybrids 
are able to breed inter se, they transmit to their offspring 
from generation to generation the same compounded 
organisation, and hence we need not be surprised that 
their sterility, though in some degree variable, rarely 
diminishes. 
It must, however, be confessed that we cannot under¬ 
stand, excepting on vague hypotheses, several facts with 
respect to the sterility of hybrids ; for instance, the 
unequal fertility of hybrids produced from reciprocal 
crosses ; or the increased sterility in those hybrids which 
occasionally and exceptionally resemble closely either 
pure parent. Nor do I pretend that the foregoing 
remarks go to the root of the matter: no explanation 
is offered why an organism, when placed under unna¬ 
tural conditions, is rendered sterile. All that I have 
attempted to show, is that in two cases, in some respects 
allied, sterility is the common result,—in the one case 
from the conditions of life having been disturbed, in the 
other case from the organisation having been disturbed 
by two organisations having been compounded into one. 
It may seem fanciful, but I suspect that a similar 
