1916] Chandler: Structure of Feathers 257 



nating in the condition found in passerine birds and allied forms. 

 There is further evidence in support of the latter alternative in that, 

 so far as I have been able to discover, tiloplumes also are totally absent 

 in the Ratitae, while, so far as is known, they are present, associated 

 with contour feathers, in all other groups of birds. 



t) Structure. — In general structure plumules are remarkably con- 

 stant, not only on different parts of the body, but also throughout the 

 entire class of birds. On different parts of the body of an individual 

 the only appreciable modification is in size, the plumules of the larger 

 apteria usually being the largest. 



The quill in plumules is invariably short and inconspicuous. 

 The calamus, which is hollow and barrel-shaped, having a more or 

 less inflated appearance, is usually entirely imbedded in the skin. 

 The shaft is always short and poorly developed, very soon breaking 

 up entirely into barbs in a more or less fan-shaped manner, and it 

 is plainly evident, in the majority of cases, that the thin, flat, more 

 or less subtriangular shaft is to be looked upon merely as a basal 

 coalescence of the barbs. The plumules possess an aftershaft in 

 groups which are characterized by the presence of an aftershaft in 

 the contour feathers, even if only rudimentary in the latter. Since 

 many of the birds which lack an aftershaft are also devoid of plu- 

 mules, it is rare to find the latter with a single shaft. Owls, which 

 lack an aftershaft on the contour feathers, with the exception of a 

 rudimentary one in Aluco, have plumules with only one shaft, a 

 dense cluster of barbs springing from the sides and ventral lips of 

 the superior umbilicus. Pelecanus was stated by Nitzsch (1867), 

 and restated by other authors, to have plumules with no shafts. This 

 is not strictly true. Pelecanus erythrorhynchus has plumules with 

 two fairly well-developed shafts, equivalent to each other, about 

 1.6 mm. long, which possess a brown pigment, the rest of the 

 plumule being unpigmented. In Phalacocorax (P. penicillatus) , how- 

 ever, the plumules almost lack a shaft, the latter structure being 

 so rudimentary that it is actually wider than long. In the Tetrao- 

 nidae and some other galliform birds, where the aftershaft of the 

 contour feathers has its shaft very highly developed with two dis- 

 tinct vanes, the plumules have the shaft likewise developed. In 

 Lophortyx, for instance, both shafts of the plumules reach a length 

 of six or seven millimeters, in spite of the small size of the feathers. 

 As pointed out by me (1914), the shaft and aftershaft of plumules, 



