STRUCTURE OF THE HAIRS OF :\IYL0D0N LISTAI. 407 



is wanting on the basal part^ and tlie scaling there is particu- 

 larly clear. But in Mylodon the transition is very gradual, 

 the scaling becoming fainter and fainter, and giving place to 

 a uniformly stained external layer, whereas in a damaged 

 Bradypus hair the scaling disappears in sharply outlined 

 patches which do not stain at all. 



Lonnberg writes (7, p. 162) that iu tangential sections of 

 the skin he saw around some of the hairs two rings, the outer 

 of which was the epithelial hair-sheatli, while the inner he 

 took to be the " loose outer bark of the hair " — the extra- 

 cortex, in fact. Since, however, in the fully grown hairs of 

 neither Bradypus nor Choice pus is the extra-cortex found 

 within the follicle or anywhere near it, the argument fails to 

 carry as much weight as he evidently intended it to do. His 

 remarks on the following pages concerning the rings of dried 

 epithelial substance around the exposed bases of the hairs 

 are equally unfortunate. On the drying of the skin the hairs 

 become protruded, and that region of each which in life was 

 flush with the surface and closely surrounded by the general 

 epidermis is pushed some distance out, a millimetre or so, 

 dragging up the stratum corneum into the form of a cone. 

 As the cone dries it cracks horizontally at a little below the 

 summit, leaving an annulus attached to the hair. This is the 

 kind of thing which can be seen by examining with a lens 

 almost any museum skin of a mammal with a thick skin and 

 stiff hair. 



Again, a glance at the transverse section of the Bradypus 

 hair taken through its broad part (fig. 3) is sufficient to show 

 that, Avere the extra-cortex removed by disintegration or 

 rough treatment, the central core would present a very 

 ragged, unstainable edge, quite unlike the uniform, smooth, 

 and deeply staining cuticular border of the transverse section 

 of the Mylodon hair (fig. 24). And lastly, the reappearance 

 of the cuticular scaling at the tip of the Bradypus hair (fig. 

 2) is not paralleled in the hair of Mylodon. Thebulkof the 

 evidence appears, therefore, to be against Lounberg's theory, 

 and we must consider the hairs of Mylodon to be preserved 



