o which may be added the lately recorded case
of the transmission during a century of hare-lip with a cleft-palate in the
writer's own family,[64] yet other malformations are rarely or never
inherited. Of these later cases, many are probably due to injuries in the
womb or egg, and would come under the head of non-inherited injuries or
mutilations. With plants, a long catalogue of inherited monstrosities of
the most serious and diversified nature could easily be given; and with
plants, there is no reason to suppose that monstrosities are caused by
direct injuries to the seed or embryo.

_Causes of Non-inheritance._

A large number of cases of non-inheritance are intelligible on the
principle, that a strong tendency to inheritance does exist, but {25} that
it is overborne by hostile or unfavourable conditions of life. No one would
expect that our improved pigs, if forced during several generations to
travel about and root in the ground for their own subsistence, would
transmit, as truly as they now do, their tendency to fatten, and their
short muzzles and legs. Dray-horses assuredly would not long transmit their
great size and massive limbs, if compelled to live on a cold, damp
mountainous region; we have indeed evidence of such deterioration in the
horses which have run wild on the Falkland Islands. European dogs in India
often fail to transmit their true character. Our sheep in tropical
countries lose their wool in a few generations. There seems also to be a
close relation between certain peculiar pastures and the inheritance of an
enlarged tail in fat-tailed sheep, which form one of the most ancient
breeds in the world. With plants, we have seen that the American varieties
of maize lose their proper character in the course of two or three
generations, when cultivated in Europe. Our cabbages, which here come so
true by seed, cannot form heads in hot countries. Under changed
circumstances, periodical habits of life soon fail to be transmitted, as
the period of maturity in summer and winter wheat, barley, and vetches. So
it is with animals; for instance, a person whose statement I can trust,
procured eggs of Aylesbury ducks from that town, where they are kept in
houses and are reared as early as possible for the London market; the ducks
bred from these eggs in a distant part of England, hatched their first
brood on January 24th, whilst common ducks, kept in the same yard and
treated in the same manner, did not hatch till