1916] Chandler: Structure of Feathers 385 



(8) Proximal barbules of outer vane of remiges without ventral 

 cilia except at extreme tip of barbs, or with a sudden transition at 

 about middle of barb. 



(9) Looser body feathers with barbules very much reduced and 

 simplified, with all barbieels rudimentary or absent except two or 

 three booklets on distals. 



(10) Down barbules with lobate or fingerlike villi on base, the 

 pennulum with more or less distinct nodes, the latter not strikingly 

 larger near base of barbules. 



IV General Conclusions 

 1. Taxonomic Value of the Structure of Feathers 



The systematic study of the structure of feathers of different 

 groups of birds which has been made and presented in the preced- 

 ing pages cannot but impress one with the fact that the morphology 

 of feathers, in other words, the epiphyology of birds, is as valuable 

 from a taxonomic point of view as is osteology, myology, or the 

 systematic morphology of any other organ or system of organs of 

 the body. Not only is the difference between birds of different 

 groups of larger content as clearly marked in the structure of their 

 feathers as in the structure of any other system of organs, but the 

 fact that most of the modifications in these minute details of 

 structure which are found in different groups of birds can be of 

 little or no adaptive value, increases the taxonomic value beyond 

 that possessed by most other organs, since parallel or convergent 

 adaptive evolution is largely eliminated. As in all other organs, 

 parallel evolution which is not necessarily correlated with adapta- 

 tion may take place, and undoubtedly has done so, with the result 

 that the structure of feathers alone is not a safe criterion of rela- 

 tionship any more than is the structure of the bones or muscles. 

 Taken in conjunction with the evidence furnished by other organs 

 and systems of organs, however, and with these as a general guide, 

 the cases of parallelism in evolution can in most cases be discov- 

 ered, and the evidences of relationship and phylogenesis furnished 

 by the morphology of feathers is then of the very highest value. 



As has been pointed out by Cockrell (1911a), the scales of 

 fishes are unquestionably of great taxonomic value. Work on the 



