^°i'qo^^] Recent Literature. 87 



Germ'; ' B. The Differentiation of the Feather,' as (i) the barbules, (2) the 

 barbicels, (3) the barb, (4) the rhachis, (5) the residual cells, (6) the corni- 

 fication and withdrawal of the featlier. 'IV. The Production of Color in 

 the feather'; 'V. The Pigmentation of the Feather'; under which are 

 considered, (A) the chemical nature of feather pigments, (B) the origin of 

 pigment, and (C) the distribution of pigment in feathers. 'VI. Change 

 of Color without Molt'; 'VII. Summary' ; and 'Bibliography.' 



In his introduction the author sajs : "A theory of change of color with- 

 out molt was the subject of a rather warm conti"oversj about the middle 

 of the nineteenth century, and there has been something of a revival of 

 the discussion in the last few years. It has seemed to me that a solution 

 of the problem could not be attained without a thorough consideration of 

 the causes of color and its development." 



Under 'VI. Change of Coloi- without Molt,' he states: "The changes 

 in color claimed by many writers to occur without molt may be grouped 

 under two heads: (i) the destructive, and (2) the constructive. Under 

 destructive changes are included the results of abrasion and ph\sical 

 disintegration. Constructive changes include supposed regeneration and 

 rearrangement of pigment." Then follows a leference to the recent 

 writers on the subject, who have claimed change of color without molt, 

 of which he says r "Descriptions of repigmentation have been mostly 

 pure speculation. Within a few years the following remarkable expla- 

 nation of the pigmentation of the feather has been given by Keeler ('93) ": 

 which he then quotes. He cites the still more recent work of Birtwell, 

 from whom he quotes concerning the supposed rearrangement of the 

 melanin granules in the feathers of the Indigo Bunting; and also quotes 

 Chadbourne's argument for a so-called vital connection of the feather 

 with the organism. After noting the claims of these and other authors, 

 and explaining to some extent the sources of their errors, he says : "There 

 is no satisfactory evidence of the occurrence of repigmentation .... 



"Pigmentation takes place, as has been shown, at a very early stage in 

 the differentiation of the feather, when the cells composing its fundament 

 are in an active condition and in intimate relation with sources of nu- 

 trition. In the case of melanin pigments, there are branched pigment 

 cells which supply pigment in the form of rod-shaped granules directly to 

 the feather fundament. The contention for a flow of pigment from the 

 barbs into the barbules, etc. (Keeler), is at once made absurd by the fact 

 that the barbules are pig'metited before the barbs are differentiated.^ 



"Variations in color patterns are usually correlated with variations in 

 the distribution of pigment in the earlier stages of the feather's develop- 

 ment. When completed, the feather is composed of cells which have 

 been entirely metamorphosed into a firm horny substance and its pigment 

 is imbedded in that lifeless matter. The cells composing a barbule are 

 fused into a solid, more or less homogeneous structure. The pigment of 

 one portion of the barbule is as effectually isolated from that of atiother as 



^ Not italicized in the original. 



