NESTLING FEATHERS OF THE MALLARD. 617 



protected by a thin epidermic sheath. When the development 

 is carried further, it becomes evident tliat in the Mallard the 

 mesoptile consists of two sets of fibres, an outer set i-epresenting 

 a shaft, and an inner, an aftershaft, each provided with a more 

 or less distinct rhachis. Though the mesoptiles in Ducks may- 

 reach a considerable size, it is ea,siei' to make out their develop- 

 ment and structure in Geese. The wing-cjuill mesoptiles, though 

 well-developed in the Mallard, are not present in the Emden 

 goose but as PI. I. fig. 3 shows, the major wing-covert mesoptiles 

 may reach a considerable size in Geese. 



To start with, the mesoptile of a Chinese gosling looks as if it 

 jDOSsessed a calamus (PI. IV. fig. 13); the mesoptile barbs seem 

 to proceed from a tube lying immediately in front of the tip of 

 the true feather. That this tubular part represents a calamus 

 is supported by the fact that it contains several " cones," but 

 against the view that it is a true calamus is the fact that it is in 

 the act of splitting longitudinally into numerous slender cords. 

 In mesoptiles from older goslings pai-t of the tubular portion is 

 represented by tw^o perforated bands, from which proceed 

 numerous slender cords towards the wing-covert. Sometimes 

 the mesoptile in goslings splits into "two portions (PL TV. fig. 14, 

 & text- fig. 5), an outer (the shaft) extending between the shaft 

 of the protoptile and the tip of the wing-quill, and an inner (the 

 aftershaft) extending between the protoptile aftershaft and the 

 vestigial aftershaft of the wing-quill. 



It may be mentioned that in the Anseres the mesoptiles vary 

 greatly in structure-— the proximal part of the aftershaft may be 

 perfoi-ated and assume the form of a section of a relatively 

 large tube (PI. IV. fig. 14), or, like the rhachis of the shaft, be 

 represented by a simple narrow band. Though in the Mallard 

 and Chinese goslings the aftershaft, as well as the shaft of the 

 mesoptile, has usually a distinct rhachis, in Emden goslings the 

 whole of the mesoptile, as PI. 1. fig. 3 suggests, usually consists 

 of simple barbs, one or two of which are continuous with the 

 rhachis of the wing-covert shaft, while two or more end in a 

 vestigial aftershaft. The barbules of the mesoptile, like those of 

 the protoptile aftershaft, are narrow and provided with well- 

 developed cilia. In the Ringed Penguin the mesoptiles closely 

 agree in structure, but in the Ducks and Geese examined no two 

 mesoptiles were alike in structure. The mesoptile coat is probably 

 as useful now to Penguin chicks hatched within or near the 

 Antarctic Circle as it was when originally acquired, during perhaps 

 a cold phase of a glacial epoch. In the Anseres, though the 

 protoptile coat still plays an important part, the mesoptile coat 

 probably no longer counts in the struggle for existence. If this 

 is the case there is no difficulty in accounting for its being well- 

 developed in some parts but entirely absent in others, and for 

 the marked variation amongst the mesoptiles which still persist. 



The Mallard has wing-covert, as well as wing-quill, mesoptiles. 

 The mesoptiles which precede the wing-coverts in the Mallard 



