a wool and a hair fibre.  You will observe that the scales of the wool fibre are rather pointed than rounded at their free edges, and that at intervals we have a kind of composite and jagged-edged funnels, fitting into each other, and thus making up the covering of the cylindrical portion of the fibre.  The sharpened, jagged edges enable these scales more easily to get under the opposing scales, and to penetrate inwards and downwards according to the pressure exerted.  The free edges of the scales of wool are much longer and deeper than in the case of hair.  In hair the overlapping scales are attached to the under layer up to the edges of those scales, and at this extremity can only be detached by the use of certain reagents.  But this is not so with wool, for here the ends of the scales are, for nearly two-thirds of their length, free, and are, moreover, partially turned outwards.  One of the fibres shown in Fig. 10 is that of the merino sheep, and is one of the most valuable and beautiful wools grown.  There you have the type of a fibre best suited for textile purposes, and the more closely different hairs approach this, the more suitable and valuable they become for those purposes, and vice versa.  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: 

    Finest merino wool fibre. 
    Typical wool fibre. 
    Fibre of wool from Chinese sheep.

FIG. 10.]

[Illustration:  FIG. 11.]

[Illustration:  FIG. 12.]