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Show 348 SEXUAL SELECTION. PART II. ·with these species, and the males require great strength and size in order to carry the females through the air. Increased size has here been acquired in opposition to the usual relation between size and the period of development, for the males, though larger, emerge before the smaller females. We will now review the several Orders, selecting such facts as more particularly concern us. The Lepidoptera (Butterflies and l\'foths) will be retained for a separate chapter. Order, Thysanura.-The members of this Order are lowly organised for their class. They are wingless, dull-coloured, minute insects, with ugly, almost misshapen heads and bodies. The sexes do not differ ; but they offer one interesting fact, by shewing that the males pay sedulous court to their females even low down in the animal scale. Sir J. Lubbock17 in describing the Smynthurus luteus, says: "it is very amusing to see these "little creatures coquetting together. 'fhe male, which " is much smaller than the female, runs round her, and "they butt one another, standing face to face, and "moving backward and forward like two playful lambs. "Then the female pretends to run away and the male "runs after her with a queer appearance of anger, gets " in front and stands facing her again; then she turns "coyly round, but he, quicker and more active, scuttles "round too, and seems to whip her with his antennre; "then for a bit they stand face to face, play with their " antennre, and seem to be all in all to one another." Order, Diptera (Flies).-The sexes differ little in colour. The greatest difference, known to Mr. F. Walker, 17 'Transact. Linnean Soc.' val. xxvi. 1868, p. 296. CHAP. X. DIPTERA. AND HEMIPTERA. 349 is in the genus Bibio, in which the males are blackish or quite black, and the females obscure brownish-orano-e The genus Elaphomyia, discovered by Mr. vVallace 1sbi~ New Gninea, is highly remarkable, as the males are furn~shed with horns, of which the females are quite des~Itute. The horns spring from beneath the eyes, and cunousl y resemble those of stags, being either branched or pal~ated. They equal in length the whole of the body m one of t~1e species. They might be thought to serve f~r fig~tmg, but as in one species they are of a beautiful pmk colour, edged with black, with a pale central stripe, and as these insects have altogether a very elegant appearance, it is perhaps more probable that the horns serve as ornaments. That the males of some Diptera fight together is certain ; for Prof. vVestwood 19 has several times seen this with some spe~ies of Tipula or Harry-long-legs. Many observers beheve that when gnats (Oulicidre) dance in the air in a bo~y, alternately rising and falling, the males are co~rtmg the females. The mental faculties of the Diptera are pro_bably fairly well developed, for their nervous system IS more highly developed than in most other Orders of insects.20 Order, Hemiptera (Field-Bugs).-Mr. J. W. Douglas w~o has particularly attended to the British species, ha~ kmdly given me an account of their sexual differences. Th~ males of some species are furnished with wings, whilst the females are wingless; the sexes differ in the for~ of the body and elytra; in the second joints of their antennre and in their tarsi ; but as the si<Ynification 0 18 'The Malay Arcbipela"o' val. ii. 1869 p 313 19 ' • • 0 , , • • 20 Mode~·n Classdicatw~ of In~ects,' v?l. ii. 1840, p. 526. See Mr. B. T. Lowne s very mterestmg work 'Ou the Anatomy of the Blow-Fly, Musca vomitoria,' 1870, p. 14. ' |