No. 635] THE HAIR OF MAMMALS 509 



protective hair. And since the structural elements in 

 these two types of hair usually differ considerably, a 

 greater number of distinctive characters is thus avail- 

 able for comparison. However, the greater thickness 

 and deeper pigmentation of the protective hair shafts 

 make them much more difficult to work with than the 

 finer, clearer fur hairs. Moreover, the scales of the pro- 

 tective hair are often worn off to such an extent as to 

 make them also valueless as identification criteria. Figs. 

 175 to 177, and 169 to 171 show, represented to scale, the 

 structure of the scales and medulla of the fur and pro- 

 tective hair of the skunk (Mephitis mephitica), and the 

 European beaver (Castor fiber). The protective hair of 

 mammals in general, in most cases, bears cuticular scales 

 of the flattened or crenate type, and medullas of the con- 

 tinuous nodose or continuous homogeneous type. 



In identifying hair species it is necessary to compare 

 the scales and medulla from the same parts of the hairs 5 



