No. 635] THE HAIR OF MAMMALS 517 



this form the scale reaches its greatest length, as can be 

 seen by the isolated scale, Fig. 198. The shorter scale, 

 of the usual dentate type is shown in Fig. 199. 



Of the three great groups of medullas : the discontinu- 

 ous, the continuous, and the fragmental, the first seems 

 to be subject to the greatest range of modification. This 

 has been subdivided into simple, and compound types. 

 The simple, furthermore, can be grouped as : ovate, rep- 

 resented by Figs. 114 to 126, elongate, shown by Figs. 

 127 to 128, and flattened, illustrated in Figs. 129 to 135. 



The ovate type, in its various modifications, is met 

 with usually, in hairs of small diameter. Thus the hairs 

 of the shrews, moles, small rodents, one or two bats, etc., 

 possess hairs of ovate medullas. The form usually en- 

 countered is apt to be more nearly like those shown by 

 Figs. 114 to 118, than like the remainder of the ovate 

 types (Figs. 119 to 126). The latter, especially such 

 partially fused forms as shown in Figs. 120 and 121, are 

 infrequently seen. 



Still less common than these forms are the forms of 

 the elongate medullas (Figs. 127 to 128). These must 

 not be confused with the various fragmental types (Figs. 

 155 to 166). In the latter the divisions do not represent 

 regularly placed cells or chambers as in the former. 



The compound medullas, at least in the fur hairs, are 

 the least common of all. Two varieties can be easily dis- 

 tinguished; the cells of one being ovate (Fig. 136), and 

 the cells of the other flattened (Fig. 137). No instances 

 of elongate cells were observed. 



The continuous medulla (Figs. 138 to 153) seems to be 

 the one characteristic of more than half of mammal 

 hairs, particularly of those which are greater than 50/* 

 in diameter. It is found in nearly all of the protective, 

 or over hairs, and is present in all spines and bristles, in 



