164 EDWARD B. POULTON. 
tube which is open to the surface, and that the smaller 
hairs are developed in follicles which are outgrowths from 
some part of this open tube, and which do not tend to coalesce 
as in the mature animal. The distinction between chief and 
smaller hairs is subsequently lost, probably in the hairs which 
succeed those described above. In an animal of this age, how- 
ever, the first-formed hairs have not approached their full size, 
and no trace of any successional hair—either large or small—is 
to be seen. 
The existence of a distinct lumen opening on the surface at 
some distance above the apex of the hair is of such great 
morphological importance and interest in relation to the origin 
of hairs and their homology with feathers and scales, that the 
observation was confirmed again and again, by examining both 
longitudinal and transverse sections, until there could be no 
doubt about the matter. I was then anxious to ascertain 
whether the same fact held true with the larger hairs. The 
general surface of the body was valueless for this inquiry, as 
the animal was rather too old, and the tips of the large hairs 
were visible. On the under side of the tail, however, many, at 
any rate, of the large hairs (here unaccompanied by small ones) 
had not reached the surface, and there was an open tube above 
them, as in the case of the small hairs elsewhere. The probable 
bearing of this and many other peculiarities will be discussed 
at the end of the paper. 
The hairs upon the tail bear the same relation to those on the 
body as that already described in the adult. 
4. Minute Structure and Formation of Hair and its 
Sheaths. 
The hair is developed from a bulb composed, as in other 
mammals, of polyhedral cells of the rete mucosum connected 
with the superficial epidermis by an outer root-sheath, 
Protrusions of the latter give rise to apparently typical sebaceous 
glands, situated, in the smaller hairs, at the level at which the 
bundle unites to enter a common follicular neck, The upper 
