Chap. X.] DIPTERA AND HEMIPTERA. 339 



more probable that the horns serve as ornaments. That 

 the males of some Diptera fight together is certain ; for 

 Prof. Westwood 19 has several times seen this with some 

 species of Tipula or Harry-long-legs. Many observers 

 believe that when gnats (Culicidse) dance in the air in a 

 body, alternately rising and falling, the males are courting 

 the females. The mental faculties of the Diptera are 

 probably fairly well developed, for their nervous system 

 is more highly developed than in most other Orders of in- 

 sects. 20 



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 the females are wingless ; the sexes differ in the 

 form of the body and elytra ; in the second joints of their 

 antennae and in their tarsi ; but, as the signification of 

 these differences- is quite 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 com- 

 monly differ much in color ; but in about six British spe- 

 cies 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 marked 

 with vermilion and black. It is doubtful whether these 

 colors serve as a protection. If in any species the males 

 had differed from the females in an analogous manner, we 

 might hav.e been justified in attributing such conspicuous 

 colors to sexual selection with transference to both sexes. 



Some species of ReduvidaB make a stridulating noise ; 



19 'Modem Classification of Insects,' vol. ii. 1840, p. 526. 

 80 See Mr. B. T. Lowne's very interesting work, ' On the Anatomy of 

 the Blow-Fly, Musca vomitoria,' 1870, p. 14. 



