174 EDWARD B. POULTON. 
the upholders of the hair-feather homology interpret it merely 
as a precocious development of the epidermic constituent, owing 
to the greater importance of the root in the hair, while the 
corium papilla, which only becomes of importance for nutritive 
purposes at a later stage of development, is correspondingly 
delayed. Such blearing of the record is not unknown in onto- 
geny; indeed, the fact that the follicle of the hair commences 
as a solid structure with no morphological communication with 
the exterior, and only later shows a differentiation into outer 
and inner root-sheaths as the hair pushes its way through the 
superficial layers of epidermis may be, and has been, explained 
by invoking the same causes—precocious and retarded develop- 
ment. 
But another meaning has recently been given to the early 
activity of the epidermis in the formation of the hair. This 
and the various other divergences from the process occurring 
in feather-formation have been regarded as pointing to an en- 
tirely different ancestor for the hair, viz. to the epidermal sense- 
organs of fishes and Amphibia. Maurer (1892) is the parent 
of this ingenious theory, and discusses the question in a very 
complete and thorough manner. In his earliest paper he con- 
trasts the development of hair, on the one side, with that of the 
feather and scale on the other. He has examined the matter 
for himself, and finds what he regards as very essential differ- 
ences between them. 
He describes the early stages in the development of the hair 
in a variety of mammals,—cat, mouse, mole, hedgehog, Dasy- 
urus, and Perameles; and though the details may differ, he 
finds that invariably the first trace of a hair is expressed by the 
elongation of the cells of the deepest layer of the epidermis ; 
so that the forecast is sharply marked off from the surrounding 
epidermis. These elongated cells may, as in Talpa, reach 
the surface, which is here slightly pitted (giving an appearance 
exceedingly similar to that of an early stage of an Ichthyopsid 
sense-organ). Usually, however, the superficial flattened cells 
of the epidermis are continued over the tops of the elongated 
cells. The modification of cells indicating a corium papilla 
