EXTERNAL FEATURES 25 



The prepennae of the body generally (head, neck, trunk, 

 and hind limbs) are mostly protoptiles, sometimes so 

 poorly developed that they are like preplumulae. Some of 

 the trunk pennae are preceded by mesoptiles. The general 

 inference is that the second nestling coat of prepennae is in 

 process of suppression. 



The preplumules of the mallard are in most regions 

 hidden by a relatively dense coat of protoptiles. The 

 plumules usually consist of a calamus, a shaft, and an 

 aftershaft ; both shaft and aftershaft bear long slender 

 barbules marked by characteristic pyramidal swellings. 



A study of the structure and development of filoplumes 

 points to the conclusion that filoplumes are degenerate 

 pennae, nearer to protoptiles than to preplumulae ; and filo- 

 penna would be a better name than filoplume. 



The development of the aftershaft indicates that it is a 

 primary not a secondary feature. It grows from apex to 

 base, and is completed before the calamus is formed. 

 Moreover, the tip of the aftershaft is connected with the 

 calamus about to be shed. If this be the case, then a 

 complete true feather (penna), like a down feather (plumula), 

 consists of two shafts or blades. It is the reduction of the 

 aftershaft that is secondary, and Professor E wart's investiga- 

 tions show that the presence of a strong aftershaft is more 

 frequent than is usually supposed. 



Professor Ewart is strongly opposed to the view that 

 feathers evolved from scales. " It is inconceivable that the 

 small protoptile forerunners of the wing-quills of Ducks 

 were evolved from enlarged scales, which as they increased 

 in length became fimbriated. The more the history of 

 feathers is studied the more untenable becomes the belief 

 in their origin from scales." The embryological evidence 

 only shows that the feather arises, like the scale, from a 

 papilla of epidermis fed by a core of dermis. There are 

 no hints of transitions between feathers and scales. 



Of the evolution of plumage Professor Ewart gives a 

 very interesting provisional sketch. " A study of the 

 development of birds suggests : (i) that their coat, to start 



