The Descent of Man

Coleoptera. But Dr. Gruber further shews that
their development is in part directly due to the
stimulus from the friction of one wing over the
other.
[Fig.13. Chlorocoelus Tanana (from Bates). a,b.
Lobes of opposite wing-covers.]
In the Locustidae the opposite wing-covers
differ from each other in structure (Fig. 13), and
the action cannot, as in the last family, be reversed.
The left wing, which acts as the bow, lies
over the right wing which serves as the fiddle.
One of the nervures (a) on the under surface of
the former is finely serrated, and is scraped
across the prominent nervures on the upper
surface of the opposite or right wing. In our
British Phasgonura viridissima it appeared to
me that the serrated nervure is rubbed against
the rounded hind-corner of the opposite wing,
the edge of which is thickened, coloured
brown, and very sharp. In the right wing, but
not in the left, there is a little plate, as transpa-