coarser-skinned sheep never being affected.

The period of gestation was formerly thought to be so unalterable a
character, that a supposed difference between the wolf and the dog in this
respect was esteemed a sure sign of specific distinction; but we have seen
that the period is shorter in the improved breeds of the pig, and in the
larger breeds of the ox, than in other breeds of these two animals. And now
we know, on the excellent authority of Hermann von Nathusius,[232] that
Merino and Southdown sheep, when both have long been kept under exactly the
same conditions, differ in their average period of gestation, as is seen in
the following Table:--

Merinos 150.3 days.
Southdowns 144.2 "
Half-bred Merinos and Southdowns 146.3 "
3/4 blood of Southdown 145.5 "
7/8 " " 144.2 "

In this graduated difference, in these cross-bred animals having different
proportions of Southdown blood, we see how strictly the two periods of
gestation have been transmitted. Nathusius remarks that, as Southdowns grow
with remarkable rapidity after birth, it is not surprising that their
foetal development should have been shortened. It is of course possible
that the difference in these two breeds may be due to their descent from
distinct parent-species; but as the early maturity of the Southdowns has
long been carefully attended to by breeders, the difference is more
probably the result of such attention. Lastly, the fecundity of the several
breeds differs much; some generally producing twins or even triplets at a
birth, of which fact the curious Shangai sheep (with their truncated and
rudimentary {98} ears, and great Roman noses), lately exhibited in the
Zoological Gardens, offer a remarkable instance.

Sheep are perhaps more readily affected by the direct action of the
conditions of life to which they have been exposed than almost any other
domestic animal. According to Pallas, and more recently according to Erman,
the fat-tailed Kirghisian sheep, when bred for a few generations in Russia,
degenerate, and the mass of fat dwindles away, "the scanty and bitter
herbage of the steppes seems so essential to their development." Pallas
makes an analogous statement with respect to one of the Crimean breeds.
Burnes states that the Karakool breed, which produces a fine, curled,
black, and valuable fleece, when removed from its own canton near