(Fig. 12) of the teeth on the under side of the nervure of another
species of Gryllus, viz., G. domesticus. With respect to the formation
of these teeth, Dr. Gruber has shewn (36. Ueber der Tonapparat der
Locustiden, ein Beitrag zum Darwinismus, Zeitschrift fur
wissenschaft. Zoolog. B. xxii. 1872, p. 100.) that they have been
developed by the aid of selection, from the minute scales and hairs
with which the wings and body are covered, and I came to the same
conclusion with respect to those of the 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 transparent as talc, surrounded by nervures, and called the
speculum. In Ephippiger vitium, a member of this same family, we have a
curious subordinate modification; for the wing-covers are greatly
reduced in size, but the posterior part of the pro-thorax is elevated
into a kind of dome over the wing-covers, and which has probably the
effect of increasing the sound. (37. Westwood Modern Classification
of Insects, vol. i. p. 453.)
We thus see that the musical apparatus is more differentiated or
specialised in the Locustidae (which include, I believe, the most
powerful performers in the Order), than in the Achetidae, in which both
wing-covers have the same structure and the same function. (38.
Landois, Zeitschrift fur wissenschaft. Zoolog. B. xvii. 1867, ss.
121, 122.) Landois, however, detected in one of the Locustidae, namely
in Decticus, a short and narrow row of small teeth, mere rudiments, on
the inferior surface of the right wing-cover, which underlies the other
315