NElSTLlNG PEAxaERS OF THE MALLARD. 627 



primitiv'e but a secondarily acquired feature. The chief reasons 

 given for regarding the af tei^shaft as an accessory and secondarily 

 acquired structure are: (1) that the aftershaft is developed from 

 a forwai'd elongation of the calamus, and (2) that the tip of the 

 aftershaft of the new feather is never attached to the calamus of 

 the feather about to be shed — that, for example, in the Emu the 

 tip of the aftershaft of the feather of the second generation is 

 from first to last free. 



If I succeed in showing that the aftershaft, like the shaft, 

 grows from apex to base and is completed before the calamus is 

 formed and that, during development, the tip of the aftershaft 

 is connected with the calamus of the feather about to be shed — 

 is, in other words, for a time attached to the old feather — it 

 may be safely assuxaed that the aftershaft is a primitive feature, 

 and that a complete true feather (penna) like a down feather 

 (plumula) consists of two shafts or blades. 



Owen evidently assumed that a true feather was made up of a 

 calamus and a single shaft, for he states that " besides the parts 

 which constitute the perfect feather there is an appendage 

 attached to the upper umbilicus called the accessory plume " (4). 

 According to Nitzsch, the aftershaft " originates from the under- 

 side of the umbiliciform pit" (5). Gadow, in discussing the 

 aftershaft, states that when present it is developed as "a ventral 

 elongation of the calamus," and points out that if we consider the 

 various types of nestling feathers " with reference to the presence 

 or absence of an aftershaft in the Teleoptiles, we ai-e led to 

 conclude that this appendage and consequently also the double 

 feathers of certain Ratitfe are secondarily acquired not primitive 

 features " (6). 



That the aftershaft is a primaiy feature was suggested in 1903 

 by Degen in a paper on Ecdysis. In the chapter on " Adven- 

 titious Plumage," Degen writes: " I may mention here that 

 owing to the yet more primitive conditions of the feathers of the 

 trunk in some Ratitae, the extreme tips of the aftershafts, which 

 in the Cassowary and the Emu attain a length equal to that of 

 their main shafts, jointly support the new-grototh feather with 

 the latter " (7). But Degen, following Gadow, seems to adopt 

 the view that the calamus is concerned with the formation of the 

 aftershaft, for he assumes that while the one half of the calamus 

 " deposits substantia rhachidis externa for the main shaft, the 

 other half deposits" the same substance required in the building 

 up of the other shaft ! Obviously the best way to throw light on 

 the status of the aftershaft is to study its development. 



1. The Development of the Aftershaft of Plumuloi. — In the 

 Mallard a pre plumula consists of a small conical calamus, a shaft 

 usually made up of four barbs, two of which coalesce to form a 

 short rhachis, and of an aftershaft also made up of four barbs. 

 Soon after hatching the preplumulse are pushed from the skin by 

 plumulas. Some of the plumulse at the end of the fifth week, 

 though still bearing preplumulse on their tips, are 15 mm. in 



