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Show 350 SEXUAL SELECTION. PART II. 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 commonly differ much in colour; 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 marked with vermilion and black. It is doubtful whether these colours serve as a protection. If in any species the males had differed from the females in an analogous manner, we might have been justified in attributing such conspicuous colours to sexual selection with transference to both sexes. Some species of Reduvidre make a stridulating noise ; and, in the case of Pirates stridulus, this is said 21 to be effected by the movement of the neck within the pro-thoracic cavity. According to Westring, Reduvius personatus also stridulates. But I have not been able to learn any particulars about these insects ; nor have I any reason to suppose that they differ sexually in this respect. Order, Bomoptera.-Every one who has wandered in a tropical forest must have been astonished at the din made by the male Cicadre. The females are mute ; as the Grecian poet Xenarchus says, "Happy the " Cicadas live, since they all have voiceless wives." The noise thus made could be plainly heard on board the "Beagle," when anchored at a quarter of a mile from the shore of Brazil ; and Captain Hancock says it can be heard at the distance of a mile. The Greeks formerly kept, and the Chinese now keep, these insects 21 Westwood, • Modern Class. of Insects,' vol. ii. p. 4 73. CHAP. X. HOMOPTERA. 351 in cages for the sake of their song, so that it must be pleasing to the ears of some men.22 The Cicadidre usually sing d~ring the day ; whilst the FuJgoridre appear to be mght-songsters. The sound accordinoto Landois,23 who _has ~ecently studied the' subject, i~ pro.duced by th~ VIbratiOn of the lips of the spiraCles, whiCh are set mto motion by a current of air emitted from the trachere. It is increased by a wonderfull c?mplex resounding apparatus, consisting of two cavities covered ?Y scales. Hence the sound may truly ~e called a voice. In the female the musical apparatus Is present,. but very much less developed than in the male: and IS never used for producing sound. . With ~·espect to the o~ject of the music, Dr. Hartman m speakmg of the Cicada septemdecim of the United States, says,24 "the drums are now (June 6th and 7th :', 185~) heard in all directions. This I believe to beth~ " mantal summons from the males. Standing in thick chestnut sprouts about as high as my head whe "hu n d re ds were around me I observed the 'f iemal re " com.m g aroun d the drummin'g males." He adds "th"es " (A , Is "s~ason ug. 1868) a dwarf pear-tree in my garden "p10d~ced. about :fi~ty larvre of Oic. pruinosa; and I " seveial ~Imes noticed the females to alight near a male while he was uttering his clanging notes" F ··t M··11 · · 11 . u er writes to me from S. Brazil that he has oftenz hstened to ~ musica~ contest between two or three males of a Cwada, havmg a particularly loud voice and seated at a considerable distance from each other.' As 22 These particulars are taken from Westwood's 'Mod Cl Insects,' vol. ii. 1840, p. 422. See also on th . ern . ass. of Spence, ' Introduct.' vol. ii. . 401, ' e Fulgondre, Kirby and "3 ' z "t hr" p . ; 4 e1 ~c 1ft fiir wissenschaft. Zcolog.' B. xvii. 1867 s 152-158 I am mdebted to Mr Walsh for ha · '. · · a' Journal of the Doings ~f Cicada septe;~~c~=,~ {;ye~~~l. sHeaxrt tmraactn .f rcm |