ncapable of its proper function of producing offspring identical
with the parent-form. Now hybrids in the first generation are descended
from species (excluding those long cultivated) which have not had their
reproductive systems in any way affected, and they are not variable; but
hybrids themselves have their reproductive systems seriously affected,
and their descendants are highly variable.

But to return to our comparison of mongrels and hybrids: Gartner
states that mongrels are more liable than hybrids to revert to either
parent-form; but this, if it be true, is certainly only a difference in
degree. Gartner further insists that when any two species, although
most closely allied to each other, are crossed with a third species,
the hybrids are widely different from each other; whereas if two very
distinct varieties of one species are crossed with another species, the
hybrids do not differ much. But this conclusion, as far as I can make
out, is founded on a single experiment; and seems directly opposed to
the results of several experiments made by Kolreuter.

These alone are the unimportant differences, which Gartner is able to
point out, between hybrid and mongrel plants. On the other hand, the
resemblance in mongrels and in hybrids to their respective parents,
more especially in hybrids produced from nearly related species, follows
according to Gartner the same laws. When two species are crossed,
one has sometimes a prepotent power of impressing its likeness on the
hybrid; and so I believe it to be with varieties of plants. With animals
one variety certainly often has this prepotent power over another
variety. Hybrid plants produced from a reciprocal cross, generally
resemble each other closely; and so it is with mongrels from a
reciprocal cross. Both hybrids and mongrels can be reduced to either
pure parent-form, by repeated crosses in successive generations with
either parent.

These several remarks are apparently applicable to animals; but the
subject is here excessively complicated, partly owing to the existence
of secondary sexual characters; but more especially owing to prepotency
in transmitting likeness running more strongly in one sex than in the
other, both when one species is crossed with another, and when one
variety is crossed with another variety. For instance, I think those
authors are right, who maintain that the ass has a prepotent power over
the horse, so that both the mule and the hinny more res