x 
246 FEATHERS 
pimple or “ feather-papilla” multiply rapidly and cause it to take 
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the shape of a cone, 
the apex of which 
is directed backward. 
The base of the papilla 
then sinks more deeply 
into the skin, chiefly 
owing to the down- 
ward growth of the 
““s-, mass of Malpighian 
cells, which arrange 
themselves into two 
halves—an (1) outer 
one, lining the invagin- 
ated mass of cells of 
the “ feather-follicle” 
and directly continuous 
with the Malpighian 
stratum at the surface; 
and (2) an inner one 
which, like a mantle, 
surrounds the whole 
LONGITUDINAL SECTION OF A VERY YOUNG TELEOPTILE central mass This 
or A Piceon. Magnified. 
C, Cutis; ZH, Epitrichium; J/, Malpighian cells; 141, 
mass or “pulp” is 
Middle stratum of inner half of the Malpighian mass of cells ; wholly a product, of 
M.F. Outer half of Malpighian cells forming the follicle; P, the cutis, and therefore 
Pulp; Rm, Rami; Sh. Sheath; St.c./.Stratum corneum of the 
follicle continued into St.c. at the surface of the skin. 
of mesodermal origin, 
and its upper portion 
is gradually transformed into a delicate meshwork which 1s 
filled with blood—the plasma necessary for the nutrition of the 
epidermal parts. In fact, the pulp is 
the nutritive organ of the whole 
feather. 
The mantle of Malpighian cells 
which surrounds the pulp differentiates 
itself into three strata of unequal thick- 
ness. The innermost and thinnest 
stratum forms a transparent sheath for 
the pulp, and persists ultimately as 
the series of “caps” or “soul” before 
mentioned. The middle stratum is 
the thickest and becomes the feather 
itself, while the outermost forms a 
transparent and coherent cylindrical 
sheath, which encloses the growing 
TRANSVERSE SECTION OF THE SAME 
FEATHER THROUGH 1). Magnified. 
A.S. Cells forming the future After- 
shaft ; C, Cutis; J’... Malpighian cells 
of the follicle; P.S. Cells of the prin- 
cipal shaft; R, Rami; Sh. Sheath ; 
St.c.F. Stratum corneum of the follicle. 
feather, giving it its well-known spine-like appearance, until, peeling 
