I 
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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. V, fig. 5). The question of the formation 
of these racket - feathers has been broached by several writers, 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 1879, 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. Prof. W. 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 (cf ad. P. platurus) 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 VI, fig. 3 displays 44 mm of a growing shaft (cf ad. P. Jlavicans)^ 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 
