514 THE AMEBIC AX NATURALIST [Vol. LIV 



power to resolve the scale outlines, or the structure of 

 the medulla, but one portion of the cylindrical hair shaft 

 can be brought into exact focus at a time. The objective 

 must in focusing follow around tin' hair, as it were, up 

 one side, and down the other, revealing, as it goes, the 

 course of the outline of the scale, or of the irregularities 

 of the medulla. The resulting curves are then drawn on 

 the single plane of the paper, as though the hair had, by 

 some means, been crushed out flat without distorting its 

 structure. It is because of this rotundity of the various 

 elements of the hair shafts that it is often impossible to 

 secure adequate photomicrographs of hair shafts, since 

 it is necessary to employ high-powered objectives with a 

 consequent very limited focal depth. Moreover the 

 various different indices of light refracti#n and reflec- 

 tion among the hyaline elements of the shaft produce, 

 upon the finished photograph, various striations and 

 markings of one sort and another, which have no anal- 

 ogue in the actual structure of the hair shaft itself. It 

 is possible, however, that photomicrographs of small. 



livery useful in determining the form and placentation 

 pattern of the pigment granules. 



The figures of the fur hairs are arranged with the sim- 

 ple form of each type of scale, or medulla, coming first, 

 followed by its various common variations. The hair of 

 the civet (Arctogalidia fusca) (Fig. lj represents the 

 simplest form of the imbricate scale, termed the ovate. 

 Fig. 17!) shows the normal appearance of a single isolated 

 scale of this type. Figs. 2 to 7 show the commonest modi- 

 fications which the ovate scale undergoes. Of all of the 

 imbricate scales whose longitudinal axis is equal to, or 

 greater than, the transverse axis, the ovate is the most 



Between the ovate scale and the acuminate, no definite 

 line of demarcation can be drawn. I have considered 

 Figs. 8 and 9 to represent perhaps the simplest form of 

 the acuminate type. Figs. 10 to 17 show scales of in- 



