. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings -- Origin. Chap. X.] ORTHOPTERA. 343 ; 29 Dr. Scudder was able to excite one of these in-' sects to answer him, by rubbing on a lile with a In both sexes a remarkable auditory apparatus has been discovered by Von [Siebold, situated in the front In the three Families the sounds are differently pro- duced. In the males of the Achetidse both wing-covers have the same structure; and this in the field-cricket (
. The descent of man, and selection in relation to sex. Evolution (Biology); Sexual selection in animals; Sexual dimorphism (Animals); Sex differences; Human beings -- Origin. Chap. X.] ORTHOPTERA. 343 ; 29 Dr. Scudder was able to excite one of these in-' sects to answer him, by rubbing on a lile with a In both sexes a remarkable auditory apparatus has been discovered by Von [Siebold, situated in the front In the three Families the sounds are differently pro- duced. In the males of the Achetidse both wing-covers have the same structure; and this in the field-cricket (Gryllus campestris, fig. 10) consists, as described by Landois,32 of from 131 to 138 sharp, transverse ridges or teeth (st) on the under side of one of the nervures of the wing-cover. This toothed nervure is rapidly scraped across a projecting, smooth, hard nervure (r) on the upper surface of the opposite wing. First one wing is rubbed over the other, and then the movement is reversed. Both wings are raised a little at the same time, so as to increase the resonance. In some .Species the wing-covers of ,^ie males are furnished at the base with a talc-like I have here given a drawing (fig. 11) of the teeth on the under side of the FlG Teeth of nervure of another species of Gryllus, viz., ?0eSticu8G(from G. domestiCKS. Landois). In the Locustidse the opposite wing-covers differ in structure (fig. 12), and cannot, as in the last family, be in- differently nsed in a reversed manner. The left wing, which acts as the bow of the fiddle, lies over the right 29 • The Naturalist on the Amazons,' vol. i. 1863, p 252. Mr. Bates gives a very interesting discussion on the gradations in the musical appa* ratus of the three families. See also Westwood, ' Modern Class.' vol. ii. pp. 445, 453. 30 ' Proc. Boston Soc. of Nat. Hist.' vol. xi. April, 1868. 31 ' Nouveau Manuel d'Anat. Comp.' (French translat.), torn. i. 1850, p. 567. 32 ' Zeitschrift fiir wissenschaft. Zoolog.' B. xvii
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