76' Introduction: Variation. 



4. llackets arc ])resent in birds having no affinity with one another, and 

 in the most varied jjositions 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, Maaodipteri/x , on the overreaching 

 tail-feathers of J^rioiiitiaus, of the Indian Drongos, Bhriuga and Dissemurua the 

 web of the racket on the outside only , of the Kingfishers of the genus 

 Tanj/ttipfi'tii, etc. 



5. Remains of the web are often to be found on the shaft of the racket 

 (pi. V, fig. 5). 



6. There a])pears to be no other means of accounting for the origin of 

 these racket-fcatliers. 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. Prionitunis platurua and Jiavicaiis). 



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. 'I'he 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 youug 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 ])ositiou 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 

 Priouiturus, but attenuated for its terminal projecting portion and for a little distance 

 on the non-projecting part ,see plate VIII. fig. I). These attenuated ends are 

 not formed by attrition at the sides during the lifetime of the indiA^dual, as is 

 shown by young feathers sprouting out of the follicles thus perfectly developed 

 (see pi. Vin, figs. 2, 3). Yet the argument for attrition continued during gene- 



