This seems to show us, in the first place,
that variations in the mutual relations of the reproductive organs of
different individuals must be as frequent as structural variations have
been shown to be; and, also, that sterility in itself can be no test of
specific distinctness. But this point will be better considered when we
have further illustrated and discussed the complex phenomena of
hybridity.
_Cases of the Fertility of Hybrids, and of the Infertility of Mongrels._
I now propose to adduce a few cases in which it has been proved, by
experiment, that hybrids between two distinct species are fertile _inter
se_; and then to consider why it is that such cases are so few in
number.
The common domestic goose (Anser ferns) and the Chinese goose (A.
cygnoides) are very distinct species, so distinct that some naturalists
have placed them in different genera; yet they have bred together, and
Mr. Eyton raised from a pair of these hybrids a brood of eight. This
fact was confirmed by Mr. Darwin himself, who raised several fine birds
from a pair of hybrids which were sent him.
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