states that in Paraguay horses of various colours are
often born with their hair curled and twisted like that on the head of a
negro. This peculiarity is strongly inherited. But what is remarkable is
that the hoofs of these horses "are absolutely like those of a mule." The
hair also of the mane and tail is invariably much shorter than usual, being
only from four {326} to twelve inches in length; so that curliness and
shortness of the hair are here, as with the negro, apparently correlated.

With respect to the horns of sheep, Youatt[814] remarks that "multiplicity
of horns is not found in any breed of much value: it is generally
accompanied by great length and coarseness of the fleece." Several tropical
breeds of sheep, which are clothed with hair instead of wool, have horns
almost like those of a goat. Sturm[815] expressly declares that in
different races the more the wool is curled the more the horns are spirally
twisted. We have seen in the third chapter, where other analogous facts
have been given, that the parent of the Mauchamp breed, so famous for its
fleece, had peculiarly shaped horns. The inhabitants of Angora assert[816]
that "only the white goats which have horns wear the fleece in the long
curly locks that are so much admired; those which are not horned having a
comparatively close coat." From these cases we may conclude that the hair
or wool and the horns vary in a correlated manner. Those who have tried
hydropathy are aware that the frequent application of cold water stimulates
the skin; and whatever stimulates the skin tends to increase the growth of
the hair, as is well shown in the abnormal growth of hair near old inflamed
surfaces. Now, Professor Low[817] is convinced that with the different
races of British cattle thick skin and long hair depend on the humidity of
the climate which they inhabit. We can thus see how a humid climate might
act on the horns--in the first place directly on the skin and hair, and
secondly by correlation on the horns. The presence or absence of horns,
moreover, both in the case of sheep and cattle, acts, as will presently be
shown, by some sort of correlation on the skull.

With respect to hair and teeth, Mr. Yarrell[818] found many of the teeth
deficient in three hairless "_Aegyptian_" dogs, and in a hairless terrier.
The incisors, canines, and premolars suffered most, but in one case all the
teeth, except the large tubercular molar on each side, were deficient. With
man s