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367 
selves; also with Lochleven trout, and from these fertile hybrids 
have been raised. 
But instances can be adduced of hybrids which have crossed 
still further than the foregoing ; and again I must refer to the 
experiments at the Regent’s Park Zoological Gardens. A zebu 
was crossed by a gayal, the resulting hybrid being crossed by an 
American bison: this double hybrid was bred from by a bison : 
and this treble hybrid was alive and well in the gardens, its 
ancestry consisting of zebu, gayal, and bison. 
Seeing that none of the three received views alluded to at 
the commencement of this paper can be maintained when 
subjected to the light of ascertained facts, it seems highly 
desirable that these investigations should be continued, as they 
raise a doubt whether hybrids, if fertile, always revert to one of 
the parent forms, or whether their infertility does not increase 
and the hybrid blood die out. It may be advanced that a 
large number of my instances are taken from fishes kept in 
a, semi-domesticated state, thus affecting their conditions of life, 
especially as regards continuing their race. But I have shown 
that American char and British trout interbreed in our streams, 
as in Cardiganshire and elsewhere.* 
Blyth, when referring to hybrids among birds, as finches, or 
those of the gallinaceous tribe, observed: “the males of all of 
which appear to have been incompetent to fecundate the eggs 
produced. Perhaps the superior size, too, of these hybrids 
generally to that of either of the parent species may be ex- 
* Much has yet to be learned why it is that animals imported into foreign 
lands may die out, as white races in India; or, on the contrary, may thrive 
more abundantly than in their native habitat, as the house sparrow in 
America, and the rabbit and trout in Australasia. In Europe we see some 
imported forms die out, in some instances due to the climate, whether they 
are domesticated or wild, but capable of domestication. New races may be 
deleteriously affected by changed local surroundings, or after a time they 
may attain the limits beyond which they will not reproduce unless fresh blood 
is imported. In some there exists a deleterious sexual influence, occasioned 
by hybridity, or else otherwise acting unfavourably on the offspring. 
