76 
Introduction: Variation. 
4. Rackets are present in birds having no affinity with one another, and 
in the most varied positions on the wing, tail, or head, where a sufficiently stiff 
feather projects so as to be liable to attrition. Thus they are found on pro- 
jecting feathers on the sides of the head in the Paradise -bird, Parotia, on the 
projecting second primary of the Nightjar, Macrodipterysc , on the overreaching 
tail-feathers of Prioniturus^ of the Indian Drongos, Bhringa and Dissemurus (the 
web of the racket on the outside only) , of the Kingfishers of the genus 
Tanysiptera^ etc. 
5. Remains of the web are often to be found on the shaft of the racket 
(pi. V, fig. 5). 
6. There appears to be no other means of accounting for the origin of 
these racket-feathers. They are not sexual characters, nor is it conceivable that 
they are useful and hence developed by natural selection. The theory of 
“recognition markings” fails, because they are not present in the young and 
because they are present and very similar in different species living in the same 
localities (e. g. Prioniturus platurus and Jiavicans) . 
7. The Motmots of America have the curious habit of forming rackets 
artificially on the lengthened middle tail-feathers by biting or tearing off the web 
behind the tip. The result appears now to be partially inherited, since a very 
pronounced narrowing of the web here is seen in young birds (see Salvin, 
P. Z. S. 1873, pp. 431, 432 with figures). The habit of tearing away the web 
also appears to be inherited, for young birds reared by hand began to tear away 
the webs of the middle tail-feathers when these had reached their full length 
(see Cherrie, Auk 1892, 323). 
As an argument against the loss of the webs through attrition during the 
individual development, it has been pointed out that when a narrow fringe of 
web is found on one side of the shaft, it is almost always on the outside that 
this occurs, where it is said that it would be most likely to get rubbed (Meyer 
and W. Blasius, 11. cc.). Due weight should, however, be given to the 
following considerations: first, birds rarely spread out their tails except in flight, 
and in the position of rest one middle tail-feather lies over the other so that 
little of the latter is seen, and the inner web of the one racket would receive 
a good deal of the pressure and friction put upon the outer web of the other; 
and second, the webs on the inside would be liable to get crossed, interlocked, 
sawed and broken by one another. 
The attenuated tail-feathers of Merops. The two middle tail-feathers 
of all the species of Bee-eaters of the genus Merops are prolonged beyond the 
others when the bird is adult; the tip is not furnished with a spatule as in 
Prioniturus^ but attenuated for its terminal projecting portion and for a little distance 
on the non-projecting part (see plate VIII, fig. 1). These attenuated ends are 
not formed by attrition at the sides during the lifetime of the individual, as is 
shown by young feathers sprouting out of the follicles thus perfectly developed 
(see pi. VIII, figs. 2, 3). Yet the argument for attrition continued during gene- 
