be to mere races or breeds, they present a marked peculiarity in the
reproductive process. If you breed from the male and female of the same
race, you of course have offspring of the like kind, and if you make
the offspring breed together, you obtain the same result, and if you
breed from these again, you will still have the same kind of offspring;
there is no check. But if you take members of two distinct species,
however similar they may be to each other and make them breed together,
you will find a check, with some modifications and exceptions, however,
which I shall speak of presently. If you cross two such species with
each other, then,--although you may get offspring in the case of the
first cross, yet, if you attempt to breed from the products of that
crossing, which are what are called HYBRIDS--that is, if you couple a
male and a female hybrid--then the result is that in ninety-nine cases
out of a hundred you will get no offspring at all; there will be no
result whatsoever.

The reason of this is quite obvious in some cases; the male hybrids,
although possessing all the external appearances and characteristics of
perfect animals, are physiologically imperfect and deficient in the
structural parts of the reproductive elements necessary to generation.
It is said to be invariably the case with the male mule, the cross
between the Ass and the Mare; and hence it is, that, although crossing
the Horse with the Ass is easy enough, and is constantly done, as far
as I am aware, if you take two mules, a male and a female, and endeavour
to breed from them, you get no offspring whatever; no generation will
take place. This is what is called the sterility of the hybrids
between two distinct species.

You see that this is a very extraordinary circumstance; one does not see
why it should be. The common teleological explanation is, that it is