184 EDWARD B. POULTON. 
and in pl. v, fig. 4, still better in that of the guinea-pig, that 
the papilla terminates superiorly in a long slender process, 
which becomes actually continuous with the interspaces be- 
tween the medullary cells, while the latter cells cover the lower 
part of the process as a single layer and are represented as 
continuous with the lowest layer of columnar cells covering 
the papilla in the region of the bulb. Until we reach the 
region where the medullary cells have shrunk and degene- 
rated, the apex of the papilla is represented as forming an axial 
tube in the base of the hair, and the medulla as its epithelial 
covering in the form of a single layer corresponding to the 
lowest layer of the epidermis. 
The gradual increase in relative length and diminution in 
diameter brought about by the necessity for warmth, have im- 
plied solidity of structure, while firmness of attachment has 
demanded the follicular invagination. Development at the 
bottom of the follicle, together with the changes in shape, 
have led to the present condition in which the structure is 
formed from the lower end instead of from the surface of a 
cylinder, the axial traces of rete remaining as a vestige of the 
past. 
Turning to more recent work, we find that Maurer seeks to 
establish a distinction between hairs and scales or feathers, in 
the elongation of the lowest epidermic cells which precedes the 
development of the former but not the latter. But he has 
never made this observation upon a Monotreme, and until this 
has been accomplished no very great weight can be attached to 
his argument. Indeed, the results which I have obtained 
afford grounds for the belief that the earliest stages of develop- 
ment will approach those of scales and feathers far more closely 
than is the case with the higher mammals. 
Some of the features especially pointed to by Maurer as 
characteristic of feathers as opposed to hairs, are equally cha- 
racteristic of the hairs of Ornithorhynchus. Thus, both in 
obliquity of direction and in distinction between an upper and 
a lower surface, the large hairs of Ornithorhynchus resemble 
feathers, 
