BILL AND HAIRS OF ORNITHORHYNCHUS PARADOXUS. 175 
appears distinctly later—in Dasyurus very much later. 
Papillee of the corium are scattered about, in many of the cases 
studied, quite independently of hair forecasts; and Maurer 
believes that these papille, even if they happen to underlie such 
forecasts, are not the true root papille of hairs. 
In the development of feather (or scale) he finds very marked 
differences ; the papille—projections of corium—are distinctly 
the first to appear, and the epidermis covering a papilla is for a 
considerable time not different from the surrounding epidermis. 
There is no elongation of cells of the Malpighian layer; the 
deepest cells are cubical, as elsewhere. The papilla, it is well 
known, as it grows outwards becomes oblique, so that upper 
(outer) and lower (inner) surfaces are distinguishable ; the epi- 
dermis is scarcely changed, but is thicker on the outer side, 
and this thickening is due to proliferation of cells in the middle 
layers—not of the deepest layers. With regard to the root- 
sheath of a hair,—suppose, he says (1893, 4), that an epidermic 
scale or feather, with its papilla, were to sink downwards into 
the corium (as a hair forecast does) then the resulting sheath 
will be simple. A deep-lying position does not necessitate a 
complex sheath enclosing the horny structures ; so that an epi- 
dermal structure, borne by a deep-lying papilla and possessing 
a complex sheath (hair), is not directly explained as a papilla 
which has sunk downwards (feather). Further, although the 
feather-sheath is fairly complex, it is very early cast off after 
the feather forecast has ruptured the apex of it; whereas the 
root-sheath of a hair persists throughout life and grows so long 
as the hair continues to grow. He gives (1893, c) an explana- 
tion of this feather-sheath—he compares it with the moulted 
cuticle of reptiles. In the case of these animals, more or less 
extensive portions of the stratum corneum are from time to 
time cast off; but before this occurs the underlying epidermis 
has formed a new “cuticle” and new stratum corneum, so that 
in section the old stratum corneum does not rest directly upon 
the new one, but is separated from it by a layer of granule- 
containing cells; below this is the new “cuticle”’ and then the 
new stratum corneum. The feather-sheath consists of an 
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