No. 635] 



THE HAIR OF MAMMALS 



513 



vary so widely in diameter (6.80/* in the hair of the in- 

 termediate bat (Mormops intermedia) (Fig. 107) ; and 

 1,177 ^ in the hair of the dugong (Dugong dug on g) (Fig. 

 159), to draw them to the same scale, and at the same 

 time to make the smaller hairs of sufficient size to show 

 clearly the cuticular scales and medullas, was obviously 

 impracticable. The arbitrary expedient was therefore 

 adopted of drawing all the hairs whose diameters were 

 equal to, or less than, 50/^ to one size, and drawing all 

 those hairs whose diameters were greater than 50 to 

 another size. In the figures the latter hairs are repre- 

 sented as being slightly greater in diameter. Such a di- 

 vision into coarse and fine hairs is not without its basis 

 in common use, for it was found that as hairs are greater 

 or less than 50 fi in diameter they are called respectively 

 coarse or fine, or stiff and soft, by perhaps the majority 

 of persons. The true spines form still a third division, 

 with which, however, we shall have nothing to do. 



Such an arbitrary representation of hair shafts, how- 

 ever, affords no appreciation of the relative or actual 

 magnitudes of the hairs. In order that this might be 

 had, therefore, the actual diameter of the fur hair of 

 each species, in micra, is given after the name in the ex- 

 planation of the plates. In each case this, obviously, is 

 approximate only, the result of averaging a large num- 

 ber of individual measurements. It was found that the 

 diameters of the hair shafts of any given individual vary 

 considerably, and that a somewhat less range of varia- 

 tion occurs among the averages of different individuals 

 of the same species. Hence it is inferred that only a 

 meager amount of significance should be attached to hair 

 magnitudes, except possibly, in large averages, and be- 

 tween large groups, i.e., families or genera. 



It must also be borne in mind that the prepared hair 

 shaft, underneath the microscope, does not reveal at any 

 one time the complete contour of the cuticular scales, or 

 medulla, as it is represented in the figures. This is due 

 to the fact, that with the objectives of sufficiently high 



