612 



PROF. J. COSSAR EWART ON THE 



but the wing-quill papillse are only beginning to make their 

 appeanince * . 



In a five weeks' duckling some of the tail-quills measure 

 50 mm., but the wing-quill rudiments at the end of the fifth 

 week only measure 4 mm. The wing of a twenty-five days' 

 MallaiTl is x^epresented in PI. II. fig. 7, natui'al size, and the 

 protoptile of a secondary wing-quill of a thii'ty-eight days' 

 Mallard in PI. II. tig. 8. Though the wing-papillae appear late 

 they soon develop into filaments — filaments of a thirteen days' 

 Mallard embryo are represented in PI. III. fig. 9. With the 

 exception of the calamus the development of the protoptile is, as 



Text-fisfure 1. 



Part of a barb from the shaft of a protoptile of a 16 days' duckling showing 

 barbules spirally twisted at their origin. X 25 dia. 



Text-figure 2. 



Distal part of a barbule of a protoptile of a 23 days' duckling 

 showing cilia. X 250 dia. 



a rule, completed before the end of the twenty-eighth day of 

 incubation, so that the vascular pulp — which made the develop- 

 ment of the nestling feather possible — may be converted into 

 bloodless pith before hatching. Even when the duckling escapes 

 from the shell the nestling coat consists of bristle-like filaments. 

 But as the duckling dries, the thin friable sheaths which pro- 

 tected the protoptiles during development disintegrate, with the 

 i-esvilt that the protoptiles expand and provide the duckling 

 with a wonderfully complete outer nestling coat. A wing-quill 



* It is conceivable that tliere is some relation between the slow development of 

 the wing and the persistence of wing-quill mesoptiles. 



