this, the more suitable and valuable they become for those purposes, and
_vice versâ_. With regard to the curly structure of wool, which
increases the matting tendency, though the true cause of this curl is
not known, there appears to be a close relationship between the tendency
to curl, the fineness of the fibre, and the number of scales per linear
inch upon the surface. With regard to hair and fur, I have already shown
that serrated fibres are not specially peculiar to sheep, but are much
more widely diffused. Most of the higher members of the mammalia family
possess a hairy covering of some sort, and in by far the larger number
is found a tendency to produce an undergrowth of fine woolly fibre,
especially in the winter time. The differences of human hair and hairs
generally, from the higher to the lower forms of mammalia, consist only
in variations of size and arrangement as regards the cells composing the
different parts of the fibre, as well as in a greater or less
development of the scales on the covering or external hair surface.
Thus, under the microscope, the wool and hairs of various animals, as
also even hairs from different parts of the same animal, show a great
variety of structure, development, and appearance.

[Illustration: FIG. 5.]

[Illustration: FIG. 6.]

[Illustration: FIG. 7.]

[Illustration: FIG. 8.]

[Illustration: FIG. 9.]

[Illustration: