154 EDWARD B. POULTON. 
in their passage to the surface are exceedingly characteristic 
in appearance (figs. 13 and 15). 
The cylinder itself is hair-like in structure, being composed 
of elongated fusiform cornified cells in which traces of a nu- 
cleus, surrounded by pigment, can be detected (fig. 8). The 
lumen of the duct traverses the axis of the corneous cylinder, 
and is star-like in transverse section (figs. 9 and 10). The 
cells near the cylinder are disposed in concentric circles round 
it (fig. 9). Tracing the cylinder downwards into the inter- 
papillary process, we find many points of resemblance to a hair. 
The general epidermis is continued over it as a sheath, which 
strongly suggests the outer root-sheath of a hair, and between 
it and the cylinder itself a line of separation tends to appear 
(fig. 8, 0.7..s., and also at level c; see also fig. 10). Below, 
this sheath forms the outer part of the bulb, and is separated 
from the inner part by a space containing small branched cells, 
the nature of which could not be determined in my material 
(fig. 8, sp., and fig. 13). The cells of this outer sheath are 
richly pigmented, like, or even more than, those of the lower 
layer of the general epidermis with which they are continuous 
(figs. 8 and 10). Within this sheath the cylinder is surrounded 
by a distinct layer composed of flattened cells, shown by trans- 
verse sections to be two or more deep, but varying in thickness 
in different parts (fig. 10, fig. 11, c.; compare also fig. 8, c.). 
This layer may represent the inner root-sheath, or the cuticle 
of the hair, or both of these together. It is continued over the 
inner part of the bulb, and separates the latter from the space 
described above (fig. 8, sp.). Within this layer the cylinder 
consists, as described above, of fusiform corneous cells arranged 
longitudinally ; below, these elements pass into polyhedral cells, 
staining in carmine, &c. The inner part of the bulb is made 
up of these latter, and presents the strongest possible 
resemblance to the bulb of a hair (figs. 8 and 11). In 
certain slender cylinders which occur intermixed with the 
others, this part of the bulb appears to be wanting (fig. 15). 
In the upper part of the bulb, and for a variable distance 
above it, the duct is lined by a single layer of distinct cubical 
