1916] Chandler: Structure of Feathers 261 



young and adult, as well as of the back and breast of a cassov/ary, 

 failed to show any filoplumes whatever. What Nitzsch very probably 

 mistook for filoplumes are the tips of feathers just growing out, which 

 give exactly the appearance described by him for filoplumes. 



When present these anomalous feathers are always associated 

 with contour feathers, though not always accompanying all feathers 

 of this type; in Circus hudsonius, for instance, they could be found 

 only in the dorsal, lumbar, and caudal tracts. When present they 

 grow out in groups from the dorsal side of the socket of the contour 

 feather with which they are associated. There may be only one or 

 two of these in a group, or as many as ten in some water birds, ac- 

 cording to Nitzsch (1867). In Circus hudsonius there are from five 

 to eight in a bundle, no two in a bundle usually being of the same 

 length. 



2. Structure 



As shown by Pycraft (1909), filoplumes are really degenerate 

 feathers, only the barbs of the extreme tip of the feather becoming 

 attached to the slender shaft. The other barbs are formed more or 

 less perfectly, but through a defect in development never become 

 attached to the shaft. Nitzsch reports a case in which some downy 

 barbs and barbules were found near the base of the filoplumes in a 

 specimen of " Gallus hankiva domestica." It is very probable that 

 this was an abnormal case in which the development was not arrested 

 as usual, or it may have been a filoplume which had not completed 

 its development, and had not yet lost its deciduous barbs. 



Unlike either plumules or contour feathers, filoplumes never have 

 the quill divided into calamus and shaft, the base not becoming hollow 

 and pithy, and the superior umbilicus being absent. The only differ- 

 entiation at the base of a filoplume is a slight widening and flattening 

 (see Chandler, 1914, pi. 16 fig. 2). 



As a rule, full-grown filoplumes have exceedingly slender shafts, 

 often ridged and pitted to give a silvery appearance like a fiber 

 of silk, and they are naked except at the extreme tip, where a few 

 rudimentary barbules are borne directly on the shaft, or on two 

 or three rami which may be given off. In some species they are 

 pigmented, e. g., in the robin, Planesticus migratorius, while in closely 

 allied species, e. g., the bluebird, Sialia mexicana occidentalis, they 

 have the typical, unpigmented, silvery color. 



