PARASITIC WEAVE RBIRDS 137 



on the floor of the mouth. The pociihar rectricial growth appears 

 to be a significant character, especially because rectricial elongation 

 has developed in parallel but different ways independently in widely 

 dissimilar genera of the family. So unusual is this development in 

 Steganura that it is given in detail in the following paragraphs. 



In Steganura the median pair of rectrices not only have the wobs 

 greatl,y broadened, but their shafts are twisted 90 degrees so that 

 the lower surfaces of the webs are opposed to each other. These 

 broadened plumes are comparatively short and end in a filamentous 

 prolongation of the shaft. The next pair are much longer and have 

 their webs widened all along, narrowing somewhat terminally, and 

 hang down in a crescentic curve. Furthermore, each of these feath- 

 ers has, springing from near its base, a hairlike filament of the same 

 length as the feather. This filament, first described by Brisson 

 (1760, p. 123) and later more fully by Strickland (1850, pp. 88-91, 

 149), originally adheres to and runs along the margin of the outer 

 web, and detaches and is shed only when the feather has attained 

 its full growth. 



Since Stricldand's description and illustration (see my fig. 3) seems 

 to have been generally overlooked (his publication is not widely avail- 

 able), I quote from it in some detail. Speaking of the long, sub- 

 medial rectrices he noted : 



They differ from all the other tail-feathers in presenting a serrated appearance 

 at their margins. In the other feathers the barbs end in fine points, so that the 

 webs which they compose terminate in an acute margin. But in this particular 

 pair of rectrices, the barbs terminate abruptly, with an obliquely flattened disk 

 at the extremity of each, and the webs composed of those barbs are consequently 

 both blunt and serrated at the margin. 



On examining these feathers when in a half-grown state, a singular hair-like 

 filament is seen to spring from their base, which explains the cause of these mar- 

 ginal serrations. This filament is narrow, flat, and thin, much resembling in 

 appearance the barbs of the feathers, but reaching to three or four inches in length. 

 Its distal extremity is free; but toward the base of the half formed feather it is 

 seen to adhere to the extremities of all the barbs on one . . . side of the feather, 

 forming a conspicuous margin or "selvage" to the web. Toward the base of the 

 feather, where the imperfectly formed barbs are collected, as in all young feathers, 

 into a cylindrical bundle, and inserted into a membranous sheath, the barbs be- 

 longing to both webs of the feather are seen to be connected at their extremities to 

 the opposite sides of this intermediate filament. As the feather grows and the 

 barbs become mature, their tips are gradually released from this connecting fila- 

 ment, those of the lower or exterior web first, and those of the interior one sub- 

 sequently. Hence the distal portion of the filament becomes free and waves 

 loosely in the air. It is probable, that when the whole feather reaches maturity, 

 the filament is shed altogether. 



The cicatrices, or points of junction between the tips of the barbs and the flat 

 surface of the filament, produce a succession of slight indentations on both sides 

 of the latter, and give it a serrated appearance, which is further increased by the 



