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Show 378 SEXUAL SELECTION. PAnT IL many have the power of stridulating when excited; many are furnished with the most extraordinary horns, apparently for the sake of ornament; some which are diurnal in their habits are gorgeously coloured; and, lastly, several of the largest beetles in the world belong to this family, which 'Yas placed by Linnrous and Fabricius at the head of the Order of the Coleoptera.67 St1·idulating organs.-Beetles belonging to many and widely distinct families possess these organs. The sound can sometimes be heard at the distance of several feet or even yards,68 but is not comparable with that produced by tho Orthoptera. The part which may be called the rasp generally consists of a narrow slightlyraised surface, crossed by very fine, parallel ribs, sometimes so fine as to cause iridescent colours, and having a very elegant appearance under the microscope. In some cases, for instance, with Typhrous, it could be plainly seen that extremely minute, bristly, .scale-like prominences, which cover the whole surrounding surjace in approximately parallel lines, give rise to the ribs of the rasp by becoming confluent and straight, and at the same time more prominent and smooth. A hard ridge on any adjoining part of the body, which in some cases is specially modified for the purpose, serves as the scraper for the rasp. The scraper is rapidly moved across the rasp, or conversely the rasp across the scraper. These organs are situated in widely different positions. In the carrion-beetles ( N ecrophorus) two parallel rasps (r, fig. 24) stand on the dorsal surface of the fifth abdominal segment, each rasp being crossed, as described by Landois,69 by from 126 to 140 fine ribs. These 6i Westwood, 'l\'lodcrn Class.' yol. i. p. 184. 68 Wollaston, On certain musicnl Cmculioni<lre, 'Annals and 1\ino-. of Nnt. Hist.' vol. vi. 1860, p. H. . 0 IW 'Zeitschrift fi.i.r wiss. Zoolog.' B. xvii. 1867, s. 127. C.:IIAr. X. COLEOPTERA. 379 ribs are scraped by the posterior margins of the elytra, a small portion of which projects beyond the general outline. In many Crioceridro, and in Clythrct 4-punctata Fig. 21. Nccrophorus (from Lnndois). ?', The two rneps. Left-band figure, part of the rasp highly magnified. (one of the Chrysomeliclro), and in some Tenebrionidn:, &c.,70 the rasp is seated on the dorsal apex of the abdomen, on the pygidium or pro-pygidium, and is scraped as above by the elytra. In Heterocerus, which belongs to another family, the rasps are placed on the sides of the first abdominal segment, and are scraped by ridges on the femora.71 In certain Curculionidoo and Oarabidre? the parts are completely reversed in position, iO I am greatly indebted to Mr. G. R. Crotch for l1aving sent me nm:~e~·ous prepared specimens of various beetles belonging to these three fan:1hes and others, us well as for valuable information of all kinds. He b~heves that the power of stridulation in the Clythra has not been previOusly observed. I am also much indebted to Mr. E. W. Janson, for information and specimens. I may adtl that my sou, l\'lr. F. Darwin, finds that De1·mestes mun'nus stridulates, but he searched in vain for the apparatus. Scolytus has lately been described by Mr. Algen as a stridulator, in the' Edinburgh Monthly Mag<tzine,' 1869, Nov., p. 130. it Schiodte, translated in 'Annals and Mag. of Nat. Hist.' vol. xx. 1867, r. 37. iZ Westring has described (Kroyer, 'Naturhist. Tidskrift,' B. ii. 1848- 49, ~·- 334) the stridulating organs in these two, as well us in other famlh.es. In ~he Carabidre I have examined Elaphrus uliginosus and Bleth1sa multtpunctata, sent to me by Mr. Crotch. In Blethisa the transverse. ridges on th~ furrowed border of the abdominal segment do not come mto play, as far as I could judge, in scraping the rasps on the clytra . . |