Ol'vKilX OV FEATHERS FROM SCALES. 265 



and are like the down feathers which cover the body and wings 

 of the chick, only less in size. The smaller filaments on the 

 other scales have not expanded, but have already begun to atrophy 

 and soon disappear, while the expanded tufts drop out or break 

 away. No trace of the scale-feathers is therefore to be found 

 in chicks after they are about a month old. 



Vertical sections (PI. V, Figs. 4 and 5) show that the feather 

 filaments are direct upgrowths of the flat scales; the different 

 layers of the epidermis of the feather are continuous with and of 

 the same character as those of the scale, and the underlying 

 dermis of the one is inseparable from that of the other. Later, 

 the feather filament grows down into the skin, forming a socket 

 or follicle, and then presents the appearance of growing out 

 through a perforation of the scale, though no break in the 

 continuity of the epidermis occurs (Fig. 5). 



Similar relationships of scale and feather have been found to 

 hold in the feathered legs of poulti-y and- pigeons. The mature 

 feather appears as an outgrowth through the scale. Where, as 

 in the case of the barn owl (Strix fiamniea), feathers appear as 

 if growing out from under the scales, it is manifest that they have 

 arisen from near the margin of the scales, and that their later 

 downgrowth is a secondary relationship, as in feathers generally. 



Discussion. 



The details briefly given are restricted to the actual appear- 

 ances as regards the origin and relationships of feathers to scales 

 in the ostrich chick. Where, however, we attempt an interpre- 

 tation of the relationships, two wholly divergent views have to be 

 considered. First, we may hold that, in the course of evolution, 

 feathers have originated directly from scales; that scales have, 

 as it were, become transformed into feathers; that the feathers 

 of birds are nothing more than the modified, frayed-out scales of 

 reptiles. Second, we may regard feathers as wholly new and 

 independent formations, quite apart from scales in their origin, 

 but for their expi'ession necessarily making use of the same 

 germinal layers as scales. 



The first view is that which has hitherto prevailed among 

 zoologists, and is conforn:iable with the usual interpretations 

 adopted in studies of homology and comparative morphology, 

 upon the foundations of which the theory of organic evolution 

 has been largely erected. Homology attempts to establish the 

 similarity in origin and nature of structures seemingly diverse. 

 It proceeds on the assumption that during the course of evolution 

 structures have gradually undergone certain divergences and 

 transfonriations, but yet remain the same in their fundamental 

 nature. Hitherto, scarcely anyone has questioned that feathers 

 have evolved from scales. The only divergence has been as to 

 the process by which the change has been accomplished; but the 

 details presented by the ostrich would appear to leave no doubt 

 as to this. Following the ordinary interpretations of homology, 

 it would be accepted that scales have become transformed into 



