246 



FEA THERS 



Sh. 



owing 

 ward 



pimple or " feather-papilla " multiply rapidly and cause it to take 



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 

 to the down- 

 growth of the 

 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 

 central mass. This 

 mass or " pulp " is 

 wholly a product of 

 the cutis,, and therefore 

 of mesodermal origin, 

 and its upper portion 

 meshwork which is 

 the nutrition of the 





Longitudinal Section of a very young Teleoptile 

 OF A Pigeon. Maguifled. 



C, Cutis ; E, Epitrichium ; M, Malpighian cells ; JfiiVj, 

 Middle stratum of inner half of the Malpighian mass of cells ; 

 M.F. Outer half of Malpighian cells forming the follicle ; P, 

 Pulp ; R-ni, Rami ; Sh. Sheath ; ,5f.c.F. Stratum corneum of the 

 follicle continued into St.c. at the surface of the skin. 



is gradually transformed into a delicate 

 filled with blood — the plasma necessary for 

 epidermal parts. In fact, the pulp is 

 the nutritive organ of the Avhole 

 feather. ,/'■• 



The mantle of Malpighian cells 

 which surrounds the pulp differentiates 

 itself into three strata of unequal thick- 

 ness. The innermost and thinnest 

 sti'atum 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 grooving 

 feather, giving it its well-known spine-like appearance, until, peehng 



Transverse Section of the same 

 Feather through MiM-^. Magnified. 

 A.S. Cells forming the future After- 

 shaft ; C, Cutis ; P.M. Malpighian cells 

 of tlie follicle ; P.S. Cells of the prin- 

 cipal shaft ; R, Rami ; .''/(. Sheath ; 

 St.c.F. Stratum corneum of the follicle. 



