HAIR STRUCTURE OF THE MONOTREMATA 473 
ship between the flattened hair and the fur hair. He applied 
the term ‘shield’ to the tips of the flattened hair, which suggested 
to the present writer the term ‘shield hair,’ which is here employed 
as a designation of the larger hairs, to distinguish them as a group 
from the finer, or fur hairs, in which the shield does not appear. 
Spencer and Sweet (’98-’99) declared it their belief that in 
structure and in growth, the hairs of the Monotremata are not 
different from the hairs of the members of the higher orders, 
while on the contrary, Toldt (05) maintained that hairs with 
thickened ends (the shield hairs), such as Ornithorhynchus pos- 
sesses, is to be found nowhere else among mammals. ‘This state- 
ment he retracted a year later, however, when he discovered that 
the hairs of T'achyglossus were structurally the same. 
Upon the body of Ornithorhynchus are six rather well-defined 
areas, each bearing its characteristic type of the longer protec- 
tive shield hair. The type covering the greater part of the body 
is that found upon the dorsum (fig. 1, Ff). This type occurs 
over the whole of the back, caudad of the area of truncated shield 
hair (fig. 1, C), and is regarded as the form which all of the pro- 
tective hairs of the body would assume, were not some worn off 
at the tips during growth. 
Figure 3 shows the characteric form of the dorsal shield hair, | 
and figures 13 to 31 its structure. The shield hairs upon the 
other parts of the body exhibit similar structural details, but each 
type possesses its own distinctive distribution of pigment. Of 
this distribution later mention will be made. 
The tract which is here called the area of truncated pigmented 
shield hair (fig. 1, C), bears hair possessing shields whose trun- 
cated tips indicated that they are exposed to considerable attri- 
tion. These hairs, and more particularly those between the 
eyes, contain less pigment than the dorsal shield hairs, varying 
from a light to a distinctly yellowish brown. Upon the pinnae 
of the ears and likewise over a small area immediately surround- 
ing them, the shield hair is lacking altogether, and its place is 
taken by a very fine, short, soft fur hair, a continuation of that 
occurring beneath the shield hair over the larger portion of the 
body. ‘This fur hair of the pinnae is the finest which the animal 
possesses. 
