NESTLING FEATilERS OF THE MALLARB. 631 



aftershaft of the true feather. Pycraft considered the "ribbon- 

 shaped stem" connecting the mesoptile to the aftershaft of the 

 true feathers as somewhat remarkable, because " in all other 

 instances yet known the nestling-down when attached to contour 

 feathers is attached to the rami (barbs) of the main shaft " (9). 

 When it is realised that in Penguins the mesoptile may have a 

 well-developed aftershaft the connection of the mesoptile with 

 the aftershaft of the true feathers ceases te be remarkable. 

 Though in the Ringed Penguin the mesoptile aftershaft is de-' 

 cidedly larger and more complex than the shaft, it is developed at 

 the same time as the shaft, and is directly continuous with the 

 aftershaft of the true feathers. That in Penguins the aftershaft 

 of the true feathers has the same origin as the shaft is made 

 abundantly evident when the development of the feathers of the 

 fourth generation is studied. In PI. VIII. figs. 30 & 31 we have 

 feathers from a moulting King Penguin in the Scottish Zoological 

 Park. From fig. 30 it is evident the new feather has from the 

 first been double, consisted of outer barbs representing a shaft and 

 of inner barbs in the position of an aftershaft. Had the develop- 

 ment proceeded the tip of the aftershaft would have been set 

 free when the old feather was shed. In fig. 31, the shaft having 

 been removed, the aftershaft is seen emerging from the tip of the 

 sheath which invested the growing feather. These figures show 

 that in Penguins the aftershaft of a feather of the fourth genera- 

 tion is for a time as complete as in the Emu. The aftershaft of _ 

 the mesoptile and of the first true feather of a Ringed Penguin 

 are diagrammatically represented in text-figs. 3 & 4. 



4. The Development of the Aftershaft in the Ptarmigan, the 

 Comnnon Fowl, and the Guillemot. — As already mentioned, it 

 has been suggested that in Grouse, Fowls, and other Galli the 

 feathers forming the first nestling coat may correspond to the 

 mesoptiles forming the second nestling coat of Penguins. 

 Against this view it may be pointed out (1) that unlike the 

 mesoptiles, but like the protoptiles of Penguins and Ducks, the 

 first nestling feathers of the Galli are developed in filaments; (2) 

 that in structure they are intermediate between the pi'otoptiles of 

 Penguins and Ducks ; and (3) that they are sometimes succeeded 

 by vestiges of mesoptiles. Degen mentions that in Grouse the 

 aftershaft may be two-thii'ds the length of the shaft but, as 

 PL IX. fig, 32 shows, the aftershaft in Grouse may be as long and 

 as complex as the shaft — the only difierence in the feather 

 figured apart from its width is that, as in the Emu, the 

 rhachis of the aftershaft is slightly shorter than the rhachis 

 of the shaft. In the Ptarmigan the protoptile often con- 

 sists of fifteen barbs, eight representing a shaft with a short 

 rhachis, and seven forming an aftershaft also with a short 

 rhachis. From the protoptile calamus there proceed about 

 twenty barbs, which in some cases readily separate into three 

 distinct bundles^ — a large one destined to form the tip of the shaft, 

 and two small ones which later unite to form the tip of the 



