ar with the daughter, granddaughter, and
great-granddaughter, and so on for seven generations. The result was,
that in many instances the offspring failed to breed; in others they
produced few that lived; and of the latter many were idiotic, without
sense {122} even to suck, and when attempting to move could not walk
straight. Now it deserves especial notice, that the two last sows
produced by this long course of interbreeding were sent to other boars,
and they bore several litters of healthy pigs. The best sow in external
appearance produced during the whole seven generations was one in the
last stage of descent; but the litter consisted of this one sow. She
would not breed to her sire, yet bred at the first trial to a stranger
in blood. So that, in Mr. Wright's case, long-continued and extremely
close interbreeding did not affect the external form or merit of the
young; but with many of them the general constitution and mental
powers, and especially the reproductive functions, were seriously
affected.

Nathusius gives[263] an analogous and even more striking case: he
imported from England a pregnant sow of the large Yorkshire breed, and
bred the product closely in-and-in for three generations: the result
was unfavourable, as the young were weak in constitution, with impaired
fertility. One of the latest sows, which he esteemed a good animal,
produced, when paired with her own uncle (who was known to be
productive with sows of other breeds), a litter of six, and a second
time a litter of only five weak young pigs. He then paired this sow
with a boar of a small black breed, which he had likewise imported from
England, and which boar, when matched with sows of his own breed,
produced from seven to nine young: now, the sow of the large breed,
which was so unproductive when paired with her own uncle, yielded to
the small black boar, in the first litter twenty-one, and in the second
litter eighteen young pigs; so that in one year she produced
thirty-nine fine young animals!

As in the case of several other animals already mentioned, even when no
injury is perceptible from moderately close interbreeding, yet, to
quote the words of Mr. Coate, a most successful breeder (who five times
won the annual gold medal of the Smithfield Club Show for the best pen
of pigs), "Crosses answer well for