A CASE OE ABNORMAL PLUMAGE. 



293 



simultaneously, though in three different degrees of intensity. 

 The length of the period during which these conditions obtained 

 is, presumably, approximately that required for the differentiation 

 of a portion of the shaft equal to the band shown in Fig. i. 



Professor Whitman tells me that he once had a young com- 

 mon domestic dove which developed similarly abnormal feathers. 

 This bird was underfed during the period 

 when the Juvenal plumage was developing. 

 I am inclined to accept Professor Whitman's 

 suggestion that in both cases the abnormali- 

 ties are due to malnutrition. The effects upon 

 the remiges and rectrices were comparatively 

 slight, and appear simply as a weakening in 

 pigmentation and structure, but the body 

 coverts were strikingly modified. 



The horn cylinder (Fig. 5, rj/.) is just such 

 a structure as one would expect to find if the 

 processes of differentiation in the fundament 

 of the barbs and barbules, which have been 

 described by Davies ('89), Strong (: 02), and 

 others were to be arrested temporarily. The 

 shaft, barbs and barbules are developed in 

 apartments of a cylindrical mass of epithelium 

 surrounding a central dermal papilla, and differentiation takes 

 place from the proximal end distally. Epithelial cells prolifer- 

 ated at the proximal end of the feather germ push the differen- 

 tiating epidermal cylinder distally, and cornification takes place 

 some distance from the proximal end. If the differentiation, but 

 not the cornification, should be omitted, a simple cylinder of 

 cornified tissue such as we see in the abnormal body coverts 

 would result. The appearances at either end of the horn cylin- 

 der undoubtedly represent the end of differentiation distally, and 

 at the proximal end (Fig. 6) the resumption of differentiation of 

 the normal feather elements. 



I wish here to express my thanks to Professor Whitman for 

 the material described in this paper and for courtesies received in 

 connection with the investigation. 



O 



THE MARINE BIOLOGICAL LABORATORY, 



WOODS HOLL, MASS., September 4, 1902. 



I 



1 

 i: 1 



FIG. 6. Dorsa 

 view showing fusion 

 of two barbs and a 

 barbule into a strip 

 from the cylinder of 

 undifferentiated corni- 

 fied tissue which con- 

 nects the distal ap- 

 pendage shown in 

 Fig. 5 with the main 

 body of the feather. 

 X 49- 



