1916] Chandler: Structure of Feathers 255 



Part I 

 GENERAL MORPHOLOGY 



I. Plumules 

 1. Unspecialized Plumules 



a) Occurrence and Distribution. — As remarked above, from a 

 general survey of the feathers of a large number of species of birds, 

 it is evident that certain generalizations regarding feather structures 

 may be made. It is the intention of this portion of the paper to 

 describe the general characters of various kinds of feathers, and to 

 discuss briefly the range of modifications exhibited by them and their 

 several parts. 



Plumules are small downy feathers which are usually completely 

 covered by the contour feathers in adult birds. Their distribution 

 on the body differs a great deal in different kinds of birds. They 

 may be (1) evenly distributed over the whole body, both in the ap- 

 teria, and in the pterylae between the contour feathers; (2) sparsely 

 or unevenly scattered over the whole body; (3) confined to 

 the apteria; (4) confined to the pterylae (only in Tinamidae) ; or 

 (5) absent -entirely. The table on page 256 shows the nature of the 

 distribution of plumules in the various groups of birds, the data 

 being derived from Gadow (1891), Beddard (1898), and others. 



In looking over this table it seems evident that a uniform dis- 

 tribution of plumules is to be considered a primitive condition, yet 

 in all of the ratite birds, which have usually been considered the 

 most primitive, they are absent entirely. It seems to me that this 

 may be explained in one of two ways : either that the ratite birds 

 have degenerated from a higher type and have lost their plumules 

 concomitant with a simplification of their contour feathers from a 

 pennaceous to a downy type, or that the ratite birds show a condition 

 of plumage more primitive than any other birds, and that in the 

 course of evolution the downy contour feathers of these birds devel- 

 oped along two separate lines, one leading to the soft, fluffy, almost 

 shaftless plumules in both pterylae and apteria, the other to the 

 highly specialized contour feathers in the pterylae only. Further 



