VII 
ON THE INFERTILITY OF CROSSES 
159 
own style, in any of the three forms, were either comparatively 
or wholly sterile. 1 
We have here a wonderful amount of constitutional 
difference of the reproductive organs within a single species, 
greater than usually occurs within the numerous distinct 
species of a genus or group of genera; and all this diversity 
appears to have arisen for a purpose which has been obtained 
by many other, and apparently simpler, changes of structure 
or of function, in other plants. This seems to show us, in the 
first place, that variations in the mutual relations of the repro¬ 
ductive 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. 2 In India, according to 
Mr. Blytli and Captain Hutton, whole Hocks of these hybrid 
geese are kept in various parts of the country where neither 
of the pure parent species exists, and as they are kept for 
profit they must certainly be fully fertile. 
Another equally striking case is that of the Indian humped 
and the common cattle, species which differ osteologically, and 
also in habits, form, voice, and constitution, so that they are 
by no means closely allied; yet Mr. Darwin assures us that he 
1 For a full account of these interesting facts and of the various problems 
to which they give rise, the reader must consult Darwin’s volume on The 
Different Forms of Flowers in Plants of the same Species, chaps, i.-iv. 
2 See Nature, vol. xxi. p. 207. 
