63G PROF. 3. UOSSAR EWART ON THE 



As in feather-footed birds the feather papillae are from the first as 

 distinct from the scale papillae as the hair rudiments are distinct 

 from scales, there seems no escape from the conclusion that the 

 foot feathers are not modified scales. Further, when it is realized 

 that the foot feathers often belong to a simple primitive type, 

 have the aftershaft as long as the shaft, and that in many birds 

 there are seven or more feathers occupying the position of an 

 ancestral scale, we are justified in assuming that feathers, like 

 hairs were originally intimately related to, but not derived from, 

 scales. 



As a matter of fact, believers in the scale origin of feathers 

 admit that the foot feathers of recent birds are not derived from 

 the scales from under which they project. Just as it has been 

 assumed that the aftershaft in Emu feathers is a secondarily- 

 acquired structure, it is assumed the scales on the feet of birds 

 are secondary structures. That the scales overlapping the feathers 

 of modern bii'ds were secondarily acquired and that the foot- 

 feathers were formed from the original foot-scales, are gratuitous 

 assumptions wholly unsupported by facts. 



How or when feather filaments made their appearance it is 

 impossible to say, but we may safely assume that many centuries 

 elapsed before there was evolved in each filament a more or less 

 complex feather ; needless to say that unless a filament in which 

 a feather was evolving was of more use than a simple filament, 

 natural selection took no part in providing birds with their 

 original coat of what are now familiarly known as nestling 

 feathers. On the other hand, when one bears in mind that blood- 

 vessels extend right to the tip of a feather filament, and not merely 

 a short distance into its root as in a hair, it is probable that early 

 specialization of the filaments was well-nigh inevitable. Given a 

 constant flow of blood through the axis (pulp) of the filament, an 

 inner epidermic layer capable of rapidly adding new cells to the 

 middle layer, an outer epidermic layer forming a protecting 

 sheath and, in addition, an ever increasing demand for a coat 

 capable of arresting the flow of heat from the skin, changes were 

 almost bound to take place in the bristle- like outgrowths pro- 

 jecting from under or between the scales of the remote ancestors 

 of birds. 



Judging by what takes place to-day during the development of 

 the simple protoptiles of pigeons, the first step in the making of a 

 feather probably consisted in the splitting of the middle epidermic 

 layer to form hair-like barbs. The result of this splitting of the 

 hollow cone formed from the middle epidermic layer of a pigeon 

 filament is represented in text-fig. 13. The appearance of a 

 completed pigeon pi-otoptile after escaping from its protecting 

 sheath is represented in PI. X. fig. 38. 



The protoptiles of Penguins represent a second stage in the 

 evolution of true feathers (text-fig. 3). Like the pigeon protoptiles 

 all the barbs are alike (form a tassel or umbel), but by sprouting 

 they have acquired barbules. 



