204 OJtIGIX OF FEATHERS FROM SCALES. 



the passage from scale to feather has been accompHshed. As a 

 matter of fact, we find feathers intimately associated with scales 

 on the legs and toes of a great number of birds, including many 

 breeds of poultry, domesticated pigeons, and most birds of prey. 

 Certain conditions recently observed in ostrich chicks, at about 

 the time of hatching, appear to be peculiarly convincing as to 

 the real relationship of scales and feathers, and to afford a true 

 key to the problem. 



The ostrich, as is well known, has a row of large, quadri- 

 lateral, over-lapping scales passing down the front of the tarsus 

 and continued over the big toe. In addition, the general surface 

 of the tarsus at the sides and behind is covered with very small, 

 polygonal scales, which are continued for some distance above 

 the ankle, and cease where the leg feathers begin in the chick. 

 At the place of transition, where the scales, as it were, are about 

 to pass over into the feathered part of the skin, the former 

 actually appear to give rise to feathers; we have, in fact, the 

 .appearance of feathers growing directly out of the scales. 



The scale-feathers are to be found on ostrich chicks only 

 for a week or two before and after hatching, and are more 

 conspicuous on some individuals than on others. Before the 

 chick leaves the egg they are in the form of filaments of different 

 size, but after hatching, the larger ones open out and resemble 

 the down which covers the chick generally. The greater number 

 of the filaments, however, fail to expand, and the feather germ 

 atrophies within a week or so, when the expanded feathers also 

 fall out. The down feathers of the ostrich are not of the simple, 

 primitive nature of the first feathers of birds such as the penguin. 

 They already consist of a tuft of barbs bearing small barbules, 

 and three to five of the former are longer than the others and 

 constitute the dorsal shaft, while the smaller represent the 

 ventral aftershaft. Since despite this structural complexity they 

 are still associated with scales, it is reasonable to suppose that 

 the same relationship would be all the more likely to hold at 

 the earlier stages of their evolution. 



The ap]:)earance under a low power of the microscope of a 

 portion of the skin, just before the scales leave off, is represented 

 in PI. IV, Fig. 1. Each polygonal area represents one of the 

 small leg-scales which join one another at their edges. From the 

 lower border of each projects a blunt upgrowth or papilla, which 

 partly overlaps the scale below it. Microscopical sections have 

 been'made of these, and their internal structure proves that they 

 are true feathers at a late stage of development. The conditions 

 •a little higher up the leg, where the scales actually disappear, 

 are shown in PL IV, Fig. 2. Here the scales occur only in the 

 'lower part of the drawing, while above are to be seen imexpanded 

 feather filaments of different sizes and irregularly arranged. These 

 arise from the scaleless part of the skin, and are exactly similar 

 to those which grow from the scales. On PI. V, Fig. 3, is 

 represented the appearance in an ostrich chick about a fortnight 

 after hatching. Four of the larger filaments have now opened 

 >out, and form small tufts of barbs with barbules along each side. 



