190 EDWARD B. POULTON. 
cated downwards and interlocking with the cuticular cells of 
the hair, which are imbricated upwards, gives to the hair a 
swollen base which prevents it from being drawn with ease 
through the narrow neck of the follicle. If it be forcibly torn 
out, the inner root-sheath accompanies it. When the hair is 
ultimately shed, its attachment has risen to a higher level in 
the wall of the outer root-sheath, so that it is no longer fixed 
in the manner described above. 
The suggestions and hypotheses here put forward are not the 
result of a hasty consideration of the subject, but were delibe- 
rately adopted years ago as the best explanation of the new 
facts brought out by the investigation, and their relation to 
old facts which were imperfectly understood. 
It may be fairly claimed for the views here expressed that 
they suggest a simple and probable morphological explanation 
of every structure in the hair or associated with it. The dermal 
papilla, epidermic bulb, medulla, hair-shaft, and inner root- 
sheath, all follow naturally from the invagination of a proto- 
Mammalian scale like that diagrammatically represented in 
woodcut fig. 2, while the outer root-sheath is clearly the walls 
of the pit into which the invagination took place. The further 
fact that fig. 2 is, except for the want of invagination, essen- 
tially similar to the hair of the young of the lowest mammal, 
lends additional support to the hypothesis here suggested. 
if, however, the interpretations offered in this and{other parts 
of the present paper be dismissed by the results of further in- 
vestigation upon better material, the main facts upon which 
the interpretations rest will always remain, and, yielding as 
they do a considerable store of fresh knowledge about this 
most interesting of all mammals, must always have a value. 
