578 EXTERNAL ANATOMY OF INSECTS. 
cases, the vocal apparatus of the trunk of insects: those 
of Melolontha vulgaris he describes as situated below the 
wings, and between the two segments of the alitrunk * ; 
and if you take this insect and remove the elytra, the 
mesothorax and scapulars, under the latter and below the 
wing you will find an oval convex plate, which is pro- 
bably the part he is speaking of ;—but it is better exem- 
plified, I think, in the common Dytiscus marginalis, in 
which it is very distinct as a convex subtriangular plate 
connected with the metathoraz by membranous ligament, 
covering a kind of pouch, and appearing to open and 
shut at the vertex >. 
I must here observe, with regard to the Aptera and 
Arachnida, that the trunk in them is much more simple 
than in those insects that are furnished with wings. In 
the hexapods, in the former Orders, though there are 
usually three pedigerous segments, there is no distinction 
of dorsolum, scutellum, &c. In the Scolopendride and 
Scutigera amongst the Myriapods, according to the acute 
observations of M. Savigny *,—on which, however, some 
doubt at present rests,—there is a remarkable formation, 
the whole thorax being represented by the single plate 
that follows the head, to the under-side of which are at- 
tached the first and second pair of palpz or pedipalpi, 
and the first pair of legs, representing the three pairs of 
legs of hexapods. In the Jwide the three segments that 
follow the head, each bear a szngle pair of legs, while all 
the rest bear a double one: from whence it should seem 
to follow, that these segments and their legs represent 
a Sur le Vol des Ins.c. 1. 457—. > Prate XXII. Fic. 13. ¢ +. 
© Mém. sur les Anim, sans Vertebr.45—. Hor. Entomolog. 411—. 
