The Origin oi<' FE.vTHEiis from the Scales of Beptiles. 



1 



their internal structure proves that they are true feathers in a)i 

 early stage of development. The conditions a little higher up the 

 leg, where the scales actually disappear, are shown in Fig. 2. Here the 

 scales occur only in the lower part, while above are seen unexpanded 

 feather filaments of different sizes and irregularly arranged. These 

 arise from the naked part of the skin, and exactly similar filaments 

 may also come from the scales. Fig. 3 represents the appearance in an 

 ostrich chick about a fortnight after hatching. Four of the larger 

 feather filaments have now opened out, and form small tufts of 

 barbs with barbules along each side, exactly like tlie down feathers 

 which cover the body of the chick, only they are smaller in size. 

 The smaller feather upgrowths on the other scales have not expanded, 

 and have already begun to atrophy, and soon disappear, while the 

 tufts drop out or break away. 'No trace of the scale feathers there- 

 fore are to be found in chicks after they are about a month old. 

 They appear during the early stages of development, but begin to 

 disappear after the chick hatches. 



The earliest appearance of the scales and featliers is found on 

 ostrich chicks of about twenty days' incubation. Small white spots 

 are seen on the surface of the skin, and later an upgroM^th takes place 



KiG. (J. — Section of skin of ustricli chick, in about the same condition as thatsliown 

 ill surface view in fig. 1. The section passes tlirouyh a number of scales (.>v.), 

 now distinct from one another, and in three of them a feather papilla is 

 included The featiaer at this early stage is seen to be a definite upgrowth 

 from the hind part of a scale, and can be compared with the overIa[) in scales 

 which imbricate. 



iroiii eticJi, ;iiid tlie limits of each scale become defined. Fig. 4 repre- 

 sents a microscopic section through three of tliese earliest feather- 

 scale germs, while Fig. 5 gives a somewJiat later stage where the 

 upgrowths have begun to form. Fig. 6 represents a section through 

 several scales, at about the same stage as those shown in surface 

 view in Fig. 1, from three of which very definite feather upgroAvths 

 arise; while Fig. 7 shows an older feather filament, which has already 

 begun to grow downwards into the skin to form the feather socket. 

 All these stages leave no doubt Mliatever that a scale and a feather 

 are one and the same formation. They both originate from the same 

 germ. From its hind surface the scale sends out a small upgrowth 

 which elongates into a filament, and within the filament changes go 

 on which ultimately produce a feather, lii its origin, therefore, a 

 feather is nothing more than the modified overlcvp of a scale. 



The internal changes in the filament, which ultimately result in 

 the formation of the feather, are vei-y complex, but the details are 

 beyond the scope of the present paper. Some conception of the 

 process can, however, be gained from a study of Fig. 8. This repre- 

 sents a transverse section through a developing feather filament, 



