SEXUAL SELECTION 869 



highly remarkable, as the males are furnished with horns, 

 of which the females are quite destitute. The horns spring 

 from beneath the eyes, and curiously resemble those of a 

 stag, being either branched or palmated. In one of the 

 species they equal the whole body in length. They might 

 be thought to be adapted for fighting, but as in one species 

 they are of a beautiful pink color, edged with black, with 

 a pale central stripe, and as these insects have altogether a 

 very elegant appearance, it is perhaps more probable that 

 they serve as ornaments. That the males of some Dip tera 

 fight together is certain; for Prof. Westwood" has several 

 times seen this with the Tipulse. The males of other Diptera 

 apparently try to win the females by their music : H. Miiller"" 

 watched for some time two males of an Eristalis courting a 

 female; they hovered above her, and flew from side to side, 

 making a high humming noise at the same time. Gnats and 

 mosquitoes (Culicidae) also seem to attract each other by 

 humming; and Prof. Mayer has recently ascertained that 

 the hairs on the antennae of the male vibrate in unison with 

 the notes of a tuning-fork, within the range of the sounds 

 emitted by the female. The longer hairs vibrate sympa- 

 thetically with the graver notes, and the shorter hairs with 

 the higher ones. Landois also asserts that he has repeatedly 

 drawn a whole swarm of gnats by uttering a particular note. 

 It may be added that the mental faculties of the Diptera are 

 probably higher than in most other insects, in accordance 

 with their highly developed nervous system."' 



Order, Hemiptera (Field-Bugs). — Mr. J. W. Douglas, 

 who has particularly attended to the British species, has 

 kindly given me an account of their sexual differences. 

 The males of some species are furnished with wings, while 



>» "Modem Classification of Insects," vol. ii., 1840, p. 526. 



»» Anwendung, etc., "Verh. d. n. V. Jahrg.," xxix. p. 80. Mayer, in 

 "American Naturalist," 1874, p. 236. 



" See Mr. B. T. lowne's Interesting work, "On the Anatomy of the Blow- 

 fly, Musca vomitora," ISYO, p. 14. He remarks (p. 33) that "the captured 

 flies utter a peculiar plaintive note, and that this sound causes other flies 

 to disappear." 



