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Show 384 SEXUAL SELECTION. PART u. become, in proceeding towards the apex, more and more confluent reaular and naked · so that three-fourths of the seg~ent is ~overed with extremely fine parallel ribs, which are quite absent in the female. In the females, however, of all three species of Oryctes, when the abdomen of a softenerl specimen is pushed backwards and forwards, a slight grating or stridulating sound can be produced. In the case of the Heliopathes and Oryctes there can hardly be a doubt that the males s~ridulate in order to call or to excite the females; but w1th most beetles the stridulation apparently serves both sexes as a mutual call. This view is not rendered improbable from beetles stridulating under various emotions ; we ~\:?ow ~ha~ birds use their voices for many purposes besides smgmg to their mates. 'fbe great Chiasognathus stridulates in anger or defiance; many species do the same from distress or fear, when held so that they cannot escape; Messrs. vVollaston and Crotch were able, by striking the hollow stems of trees in the Canary Islands, to discover the presence of beetles belonging to the genus Acalles by their stridulation. Lastly the male Ateuclms stridulates to encourage the female in her work, and from distress when she is removed.7'1 Some naturaHsts believe that beetles make this noise to frighten awav their enemies; but I cannot think that the quadruped; and birds which are able to devour the l~rger beetles with their extremely hard coats, would be frightened by so slight a grating sound. The belief that the stridulation serves as a sexual call is supported by the fact that death-ticks (Anobium tesselatum) are well known to answer each other's ticking, or, as I haYe 74 :M:. P. deJa Bruleric, as quoted in • Journal of Travel,' A. Murray~ vol. i. 1868, p. 135. CIIAP. X. COLEOPTERA. 385 myself observed, a tapping noise artificially made; and Mr. Doubelday informs me that he bas twice or thrice observed a female ticking,75 and in the course of an hour or two has found her united with a male, and on one occasion surrounded by several males. Finally, it seems probable that the two sexes of many kinds of beetles were at first enabled to find each other by the slight .slm:ffiing noise produced by the rubbing together of the .adjoining parts of their hard bodies; and that as the males or females which made the greatest noise succeeded best in finding partners, the rugosities on various parts of their bodies were gradually developed by means 'Of sexual selection into true stridulating organs. .i 5 Mr. J?o.ubl~day informs me that "the noise is produced by the "msect ralSlng Itself on its legs as high us it can, and then striking its " thorax five or six times, in rapid succession, against the substance -''upon which it is sitting." For references on this subject sec L<mdois 'Zeit~chrift fiir wissen. Zoolog.' B. xvii. s. 131. Olivier says (as quoted by Ku·by and Spence, 'Introduct.' vol. ii. p. 395) that the female of Pi~elia. striata produces a rather loud sound by striking her abdomen ~gamst any hard substance, "and that the male, obedient to this call, soon attends hc1· and they pair." VOL. I. 2 c |