7^ Introduction: Variation. 



prolonged much beyond the others, and in adult birds the overreaching portion 

 of these two rectrices is converted into a bare shaft tipped with a spatule of 

 ordinary web (see pi. VI, figs. 1, 4, pi. Y, fig. 5;. The question of the formation 

 of these racket -feathers has been broached by several %vriters, especially by 

 Prof. W. Blasius Ztschr. ges. Orn. 1885, pp. 212— 219, figs.. Dr. Finsch 

 remarked Papag. 1868, II, 401) that the bareness of the shafts was manifestly 

 due to the attrition of the barbs of the feathers; Meyer showed (Ibis IS79, 49^ 

 that this view, as of a direct mutilation of the individual, is incorrect, since 

 many specimens were shot by him in which the racket-feathers were growing, 

 and the bare rachis lay upon the surface of the other feathers protected from 

 foreign contact. Pi of. AV. Blasius has expressed the opinion that the shafts 

 do not grow out naked from the first, but become bare later, owing perhaps to 

 a physiological casting-ofF of the webs. 



The specimens in the Dresden Museum prove that the webs are neither 

 rubbed off. nor bitten ofF as in the case of the Motmots ^see Salvin, P. Z. S. 

 1873, p. 433). Two specimens figured on plate VI, figs. 2, 3, display the 

 growing racket as found underneath the upper tail-coverts here removed to show 

 the conditions); the shaft is already webless even where it is still enclosed in 

 the corneous husk or follicle out of which the young feather has grown, and 

 where it could of course be neither rubbed nor bitten. On removing a third 

 younger sprouting racket (cT ad. P. platiirus by the root and taking off the 

 epidermal husk pi. V, fig. 4), it was found that the web rami) is present on 

 either side of the shaft, but some of the rami appear not to be attached at all 

 but to run, soldered together, parallel to the shaft almost to its root; other rami 

 have become individually broken off or have fallen off from the shaft, and it 

 was easy to see that, as the feather grew longer, all would have fallen from the 

 shaft. In a growing racket with the shaft 35 mm cut out of the tail of an 

 adult male bird it was not possible to detect any signs of barbs with certainty. 

 Plate \'I, fig. 3 displays 44 mm of a growing shaft ( j' ad. P. flavkans), which 

 would reach a length of 67 mm (judging from the length of the other perfect 

 racket); this shaft was found to be bare down to its point of attachment by the 

 side of the oil-gland ; near the base alone some corneous matter of uncertain 

 determination, but perhaps feather-material, was adhering to it. 



These investigations tend to prove that no web at all is produced with 

 long-shafted rackets, but rackets of a lower stage of development have imperfect 

 or unattached webs which fall off before the racket is fully exposed. 



The inquiry as to how the middle tail-feathers originally began to be 

 lengthened and narrowed and finally formed into long rackets may be answered 

 by a hypothesis which, if it is a correct explanation of the facts, may be not 

 without weight in its bearings upon theories of heredity. 



It is easy to obtain a practical demonstration as to how racket-feathers may 

 be formed by holding a feather by the barrel and scraping the webs with a 

 knife; a bare stem with a spatule at the tip then quickly forms itself, the 



