318 THE DESCENT OF MAN. 



music. H. Muller* 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 (Culicida^) 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 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 accordance with their highly 

 developed nervous system, f 



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 the 

 females are wingless; the sexes differ in the form of their 

 bodies, elytra, antennae and tarsi; but as the signification of 

 these differences is 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 con- 

 siderably 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 insect- 

 ivorous animals. In some few cases 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. 



*Anwendung, etc., "Verb. d. n. V. Jahrg.," xxix, p. 80. Mayer, 

 in "American Naturalist," 1874, p. 236. 



f See Mr. B. T. Lowne's interesting work, *' On the Anatomy of the 

 Blow-fly, Musca vomitoria," 1870, p. 14. He remarks (p. 83) that 

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

 sound causes other flies to disappear," 



