626 PROF. J. COSSAR EWAUT ON THE 



Notwithstanding their small size, the prefiloplumee have the 

 structure of prepennae. They are hence not dwarfed pre- 

 plumuljB, as their name suggests, but dwarfed protoptiles. It is 

 important to note that, though several developing filoplumae may 

 be intimately related to a protoptile, they are not imbedded in 

 its sheath ; each projects from a separate pit in the skin. At 

 the end of the seventh week, when the filoplumes have reached a 

 len<i-th of about 20 mm., they are still found in contact Avith the 

 developing true feather. A filoplume from a forty-eight days' 

 duckling, still carrying the minute prefiloplume on its tip, is 

 represented in PI. V. fig. 20. At this stage the filoplume still con- 

 sists of a calamus, a shaft and an aftershaft ; but as the duckling 

 increases in size the filoplumae in connection with the wing-quills 

 degenerate. Each loses its prefiloplume, its aftershaft, and most 

 of the barbs of its shaft, with the result that, as a rule, only the 

 rhachis of the shaft and two or three vestigial terminal barbs are 

 left. . ■ 



That the filoplumes are degenerate pennte is supported by a 

 study of the foot-feathers of the Barn Owl {StrLv flammea) . In 

 a newly-hatched Barn Owl one large and two small filaments are 

 seen projecting from under the foot-scales. Soon a well de- 

 veloped protoptile escapes from the large mesial filament and 

 a minute protoptile from each of the two small filaments. In 

 course of time a simple plumose feather (metaptile), with a large 

 aftershaft, but with a rhachis which suggests a filoplume, succeeds 

 the laro'e protoptile, and typical hair-like filoplumes succeed the 

 small protoptiles. 



If further proof were needed in support of the view that 

 filoplumes are degenerate pennee, it is obtained by the examina- 

 tion of the white neck feathers which form part of the nuptial 

 plumage of Cormorants, i. e., the feathers ISTitzsch assumed were 

 tiloplumes. Instead of regarding the narrow neck feathers of 

 Cormorants as filoplumes, it would be better to regard them as 

 true feathers (metaptiles) which have undergone degeneration. 



It may be added that, notwithstanding the small size of the 

 prefiloplumfe, a microscopic examination clearly proves that they 

 are more intimately related to protoptiles than to preplumulee. 

 Seeing that the filoplumes are degenerate pennse, it might be 

 better if the name filopenna were substituted for filopluma. 



II. The Composition of Feathers. 



The feathers forming the coat of the adult Emu consist of a 

 calamus and two blades, an outer, the shaft, and an inner, 

 o-enerally known as the aftershaft; the wing- and tail-quills of 

 ducks consist of a calamus and a well-developed shaft, but there 

 is only a minute vestige of an aftershaft. Hitherto it has been 

 taken for "•ranted that a feather with only a vestige of an after- 

 shaft is more primitive than a feather with an aftershaft as long 

 and as complex as the shaft, that, in fact, the aftershaft is not a 



