paired, they produce the full number of young, and whether the latter are
perfectly fertile inter se; but, supposing that some degree of sterility were
found to exist, naturalists would simply infer that these breeds were
descended from aboriginally distinct species; and it would be scarcely
possible to ascertain whether or not this explanation was the true one.

The Sebright Bantam is much less prolific than any other breed of fowls, and
is descended from a cross between two very distinct breeds, recrossed by a
third sub-variety. But it would be extremely rash to infer that the loss of
fertility was in any manner connected with its crossed origin, for it may with
more probability be attributed either to long-continued close interbreeding,
or to an innate tendency to sterility correlated with the absence of hackles
and sickle tail-feathers.

Before giving the few recorded cases of forms, which must be ranked as
varieties, being in some degree sterile when crossed, I may remark that other
causes sometimes interfere with varieties freely intercrossing. Thus they may
differ too greatly in size, as with some kinds of dogs and fowls: for
instance, the editor of the 'Journal of Horticulture, etc.' (16/2. December
1863 page 484.) says that he can keep Bantams with the larger breeds without
much danger of their crossing, but not with the smaller breeds, such as Games,
Hamburghs, etc. With plants a difference in the period of flowering serves to
keep varieties distinct, as with the various kinds of maize and wheat: thus
Colonel Le Couteur (16/3. On 'The Varieties of Wheat' page 66.) remarks, "the
Talavera wheat, from flowering much earlier than any other kind, is sure to
continue pure." In different parts of the Falkland Islands the cattle are
breaking up into herds of different colours; and those on the higher ground,
which are generally white, usually breed, as I am informed by Sir J. Sulivan,
three months earlier than those on the lowland; and this would manifestly tend
to keep the herds from blending.