1916] Chandler: Structure of Feathers 247 



on the structure and development of feathers have appeared, but 

 need not be mentioned here. 



Throughout the literature, no general attempt has been made to 

 use differences in the morphology of the minute structures of feath- 

 ers as taxonomic or diagnostic characters. In a few cases where 

 feathers differ macroscopically and obviously from the usual type, 

 as in cassowaries and penguins, they have been considered as of 

 taxonomic value, and the presence or absence, or degree of develop- 

 ment, of the aftershaft has been so used. Jeffries (1884) realized 

 that differences in the microscopic structures of feathers existed in 

 different groups of birds, as shown by the following quotation from 

 the paper cited: "The minute structures of these (wing and tail 

 feathers) vary in different groups of birds, as I havr myself observed, 

 and has, I believe, been pointed out by Schroeder, though I have not 

 seen his paper." In Newton's Dictionary of Birds, under the article 

 on "Feather", is a similar statement as follows: "Cilia which are 

 not furnished with hooks frequently have shapes which may possibly 

 prove to be characteristic of different groups of birds". 



The only actual investigation of group differences in the micro- 

 scopic structure of feathers was done by Mascha (1904). His work 

 is accurate and suggestive as far as it goes, but he dealt only with 

 the remiges of a very limited number of species, and, as would be 

 expected from such a restricted survey, he missed entirely the taxo- 

 nomic value of certain of the most characteristic features in the 

 microscopic structure of feathers, and contributed but little towards 

 our knowledge of the systematic and phylogenetic value of feather 

 structures. 



In recent years considerable work has been done by zoologists in 

 the study of the morphology and the taxonomic value of other 

 integumentary structures of vertebrates, and their results point to 

 the fact that such structures, though constantly in contact with the 

 environment, and subject to more external influences than any other 

 organs of the body, nevertheless possess phylogenetic characters which 

 are remarkably constant and easily recognizable. 



The work of Toldt (1912) on the hair of mammals, like Mascha 's 

 (1904) work on feathers, though only a beginning, is careful and 

 accurate as far as it goes, and is highly suggestive in that it points 

 the way to a field which is still almost untouched. Work along 

 similar lines on the scales of reptiles has been done by Stehli (1910). 

 His study was rather a general treatise on a few types, designed 



