most deleterious effects. Thus, Mr. Low in his
great work on the _Domesticated Animals of Great Britain_, says: "If we
shall breed a pair of dogs from the same litter, and unite again the
offspring of this pair, we shall produce at once a feeble race of
creatures; and the process being repeated for one or two generations
more, the family will die out, or be incapable of propagating their
race. A gentleman of Scotland made the experiment on a large scale with
certain foxhounds, and he found that the race actually became monstrous
and perished utterly." The same writer tells us that hogs have been made
the subject of similar experiments: "After a few generations the victims
manifest the change induced in the system. They become of diminished
size; the bristles are changed into hairs; the limbs become feeble and
short; the litters diminish in frequency, and in the number of the young
produced; the mother becomes unable to nourish them, and, if the
experiment be carried as far as the case will allow, the feeble, and
frequently monstrous offspring, will be incapable of being reared up,
and the miserable race will utterly perish."[54]

These precise statements, by one of the greatest authorities on our
domesticated animals, are sufficient to show that the fact of
infertility or degeneracy appearing in the offspring of hybrids after a
few generations need not be imputed to the fact of the first parents
being distinct species, since exactly the same phenomena appear when
individuals of the same species are bred under similar adverse
conditions. But in almost all the experiments that have hitherto been
made in crossing distinct species, no care has been taken to avoid close
interbreeding by securing several hybrids from quite distinct stocks to
start with, and by having two or more sets of experiments carried on at
once, so that crosses between the hybrids produced may be occasionally
made. Till this is done no experiments, such as those hitherto tried,
can be held to prove that hybrids are in all cases infertile _inter se_.

It has, however, been denied by Mr. A.H. Huth, in his interesting work
on _The Marriage of Near Kin_, that any amount of breeding in-and-in is
in itself hurtful; and he quotes the evidence of numerous breeders whose
choicest stocks have always been so bred, as well as cases like the
Porto Santo rabbits, the goats of Juan Fernandez, and other cases in
which animals allowed to run wild have increased prodigio