278 THE DESCENT OP MAN. 



black, witli a pale central stripe, and as these insects have alto- 

 gether a very elegant appearance, it is perhaps more probable 

 that they serve as ornaments. That the males of some Diptera 

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

 seen this with the Tipulse. The males of other Diptera appar- 

 ently 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 (Culi- 

 cidse) also seem to attract each other by humming; and Prof. 

 Mayer has recently ascertained that the hairs on the antennsB 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 sympathetically with the graver notes, and the 

 shorter hairs with the higher ones. Landois also asserts that he 

 has repeatedly drawn down 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 ac- 

 cordance with their highly developed nervous system." 



Order, Hemlptera (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, whilst the females are wingless; the 

 sexes differ in the form of their bodies, elytra, antennae and tarsi; 

 but as the signifieation of these differences are unknown they 

 may be here passed over. The females are generally larger and 

 more robust than the males. With British, and, as far as Mr. 

 Douglas knows, with exotic species, the sexes do not commonly 

 differ much in color; but in about six British species the male is 

 considerably darker than the female, and in about four other 

 species the female is darker than the male. Both sexes of some 

 species are beautifully colored; and as these insects emit an 

 extremely nauseous odor, their conspicuous colors may serve as 

 a signal that they are unpalatable to insectivorous animals. In 

 some few case their colors appear to be directly protective: thus 

 Prof. Hoffmann informs me that he could hardly distinguish a 

 small pink and green species from the buds on the trunks of lime- 

 trees, which this insect frequents. 



Some species of Reduvidee makes a stridulating noise; and, in 



» 'Modern Classification of Insects,' vol. ii. 1840, p. 526. 



i" Anwendung, &c., 'Verh. d. n. V. Jahrg:.' xxix. p. 80. Mayer, in 

 'American Naturalist,' 1874, p. 236. 



=1 See Mr. B. T. Lowne's interesting work, 'On tlie Anatomy of the 

 Blow-fly, Musca vomitoria,' 1870, p. 14. He remarks (p. 33) that, "the 

 "captured flies utter a peculiar plaintive note, and that this sound 

 "causes other flies to disappear." 



