FEATHERS 247 
off as scurf, it sets free the rami of the young product. While 
the papilla grows to the length the young feather is to reach, the 
cells of the middle stratum arrange themselves in longitudinal rows, 
causing the pulp to assume in transverse section a somewhat star- 
shaped appearance. These rows are transformed into the hair-like 
rami of which most Neossoptiles consist, and their formation pro- 
ceeds from the apex downwards, while the radii seem to be 
produced by secondary splitting. Ultimately all the rami meet 
at the base of the feather and there form, with the basal 
portion of the sheath, a very short cylindrical tube, which is the 
calamus of the Neossoptile, while the pulp having fulfilled its 
function has withdrawn towards the base of the follicle, leaving 
only its horny sheath in the form just above stated, its projecting 
portion. 
The development of the feathers of adults is merely a con- 
tinuation of the process now described, because each Teleoptile is 
produced by the same pulp and Malpighian cells as gave rise to 
its predecessor of the first generation. The short calamus of 
a Neossoptile is not closed at its base, but is again split into a 
number of columns of cells, which though not yet horny are the 
tips of the rami of its successor. As a rule the whole follicle 
sinks deeper into the skin, and thus comes to lie in a sort of 
pocket, which, occasionally reaching the periosteum of underlying 
bones, produces on the ulna the well-known roughnesses that 
correspond with the number of cubital quills. 
Those papille which give rise to the larger feathers, such as 
the rectrices, become much thickened and greatly elongated, each 
being surrounded by a horny sheath which peals off as the feather 
attains maturity. A transverse section shews nearly the same 
conditions as those of the growing Neossoptiles, but both on the 
dorsal and ventral side are two columns longer than the rest, 
and especially the two on the former which are transformed into 
the rhachis, while the two on the latter give rise to the hypo- 
rhachis.- The intermediate columns and their secondarily-split 
parts form the rami. A transverse section of the growing feathers 
shews that both rhachis and hyporhachis pass into the calamus, 
but that the former occupies by far the greater part of the ring, 
or the whole of it when there is no hyporhachis. It is moreover 
observable in an entire quill that the rami of both outer and inner 
webs converge toward the ventral side and ultimately surround the 
umbiliciform pit. In fact, the rhachis is only a vast elongation 
and thickening of more than the dorsal half of the growing 
calamus which during its rapid increase carries with it most of the 
rami, while only those nearest the ventral median line of the quill 
remain in their original position, unless an hyporhachis. be 
developed as a ventral elongation of the calamus. The pulp 
