37 o THE POPULAR SCIENCE MONTHLY. 



bats it has developed into a sort of webbed wing. But if any of the 

 early birds happened to possess an altered hair-like or scale-like cover- 

 ing the relic, perhaps, of some common reptilio-mammalian ancestor 

 which afforded them any extra grip upon the air through which they 

 fell rather than floated, then those individuals would thereby gain an 

 extra chance of catching prey or escaping enemies, and therefore of 

 survival in the constant rivalry of species with species. The more 

 perfect these organs became, the more closely adapted to the function 

 of flight, the greater the advantage the bird would derive from their 

 possession, and therefore the better the chance of survival which it 

 would obtain. Thus, apparently, the most aerial birds have the largest 

 and strongest quills, and the most quill-like plumes, while the running 

 and diving birds have either never developed these adjuncts in their 

 highest form, or else have lost them by disuse. 



Let me take down one of the peacock's feathers, which stands on 

 the mantelpiece in this Vallauris vase, and closely examine its struc- 

 ture. It consists of a long central shaft, horny and tubular at the lower 

 end, and filled above with a soft, white, spongy matter ; while a num- 

 ber of little barbed branches are given off on either side, curiously 

 interlaced by means of tiny hooked filaments, whose myriad threads 

 are far too numerous for the most industrious critic to count up. 

 Everybody knows that this tubular structure combines in the highest 

 degree the mechanical requisites of lightness and strength ; and every- 

 body has read that it is employed with the self -same object by human 

 engineers, in such constructions as the great bridges which span the 

 Menai Straits or the St. Lawrence at Montreal. Evidently this pea- 

 cock's feather, though now converted to a purely ornamental function, 

 was originally developed for the purpose of flight. If I doubt it for 

 a moment, I need only look at the quill-pen in my desk over yonder. 

 That flat blade, close-textured and strongly woven, clearly belongs to 

 a flying organ ; and this beautiful mass of green and golden waving 

 plumelets is evidently modeled on the self-same plan. It is useless, or 

 next to useless, now, for flight ; but it still bears clear traces of its ori- 

 ginal function in the structure and arrangement of its shaft and barbs. 



Next, let me look at the little downy feather I have abstracted from 

 the Indian cushion. This is not a flying organ, nor did its representative 

 on any early ancestor ever fulfill a similar office. Light, warm, soft, 

 fluffy, its whole object is decidedly that of clothing against chilly 

 weather, and protection against thorns or other rough bodies. Yet 

 when I examine it closely, I see that the same general ground-plan still 

 runs through it, as that which ran through the goose-quill and the pea- 

 cock's tail-covert. " How comes this ? " I ask myself ; " here we have 

 a small, delicate, almost fleshy shaft, instead of the horny quill ; and a 

 feeble set of downy barbs instead of the strong, well- woven blade : yet 

 the main features remain unaltered, though the function is entirely 

 different. How can I account for this resemblance ? " 



