The Descent of Man

wing-cover, which underlies the other 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 wingcovers
had serrated nervures on the under surface,
and could be indifferently used as the
bow; but that in the Locustidae the two wingcovers
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