and is never used as the bow. I observed the same rudimentary structure
on the under side of the right wing-cover in Phasgonura viridissima.
Hence we may infer with confidence that the Locustidae are descended
from a form, in which, as in the existing Achetidae, both wing-covers
had serrated nervures on the under surface, and could be indifferently
used as the bow; but that in the Locustidae the two wing-covers
gradually became differentiated and perfected, on the principle of the
division of labour, the one to act exclusively as the bow, and the
other as the fiddle. Dr. Gruber takes the same view, and has shewn that
rudimentary teeth are commonly found on the inferior surface of the
right wing. By what steps the more simple apparatus in the Achetidae
originated, we do not know, but it is probable that the basal portions
of the wing-covers originally overlapped each other as they do at
present; and that the friction of the nervures produced a grating
sound, as is now the case with the wing-covers of the females. (39. Mr.
Walsh also informs me that he has noticed that the female of the
Platyphyllum concavum, when captured makes a feeble grating noise by
shuffling her wing-covers together. ) A grating sound thus occasionally
and accidentally made by the males, if it served them ever so little as
a love-call to the females, might readily have been intensified through
sexual selection, by variations in the roughness of the nervures having
been continually preserved.
[Fig.14. Hind-leg of Stenobothrus pratorum: r, the stridulating ridge;
lower figure, the teeth forming the ridge, much magnified (from
Landois).
Fig.15. Pneumora (from specimens in the British Museum). Upper figure,
male; lower figure, female.]
In the last and third family, namely the Acridiidae or grasshoppers,
the stridulation is produced in a very different manner, and according
to Dr. Scudder, is not so shrill as in the preceding Families. The
inner surface of the femur (Fig. 14, r) is furnished with a
longitudinal row of minute, elegant, lancet-shaped, elastic teeth, from
85 to 93 in number (40. Landois, ibid. s. 113.); and these are scraped
across the sharp, projecting nervures on the wing-covers, which are
thus made to vibrate and resound. Harris (41. Insects of New England,
1842, p. 133.) says that when one of the males begins to play, he first
bends the shank of the hind-leg beneath the thigh, where it is lodged
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