624 



PROF. J. COSSAR EWART ON THE 



is made evident by PI. Y. fig. 17, which shows a protoptile, three 

 plumulse, each with a preplumula on its tip, and, on the left 

 of the protoptile, a prefilopluma on the tip of a developing 

 filoplume. 



The preplumnla consists of a short conical calamus,' a shaft 

 often consisting of a short rhachis and four barbs, and an after- 

 shaft also as a rule consisting of four barbs. It is sometimes 

 difficult to distinguish the small protoptiles which precede small 

 true feathers from preplumulse, but when in ducklings the 



Text-figure 10. 



Filaments from a Mallard embr^-o. 



P, proximal part of a protoptile filament. P.l, a preplumula filament. 



P. 2, a prefiloplume filament. S., skin. 



barbules are characterized by nodular swellings and very fcAv 

 cilia it may be safely assumed that the nestling feather under 

 examination is a preplumula. 



(2) The Plumulce. 



At the beginning of the Jurassic Age the coat of birds may 

 have consisted only of protoptiles and preplumulae ; but in 

 many recent birds the plumula? form a very important part of 

 the nestling plumage. From PI. Y. fig. 17 it may be inferred 

 that during the fifth week the plumulaj form an inner coat as 

 effective in preventing a loss of heat as the woolly under coat of 

 wild sheep. 



