EXTERNAL ANATOMY OF INSECTS. 571 
unites with the wing; but in Scwtellera (at least so it 
is in S. signata,) it is a nearly vertical piece, marked in 
the centre with an infinity of very minute folds, which 
probably by their alternate tension and relaxation let 
out and pull in the wings. Amongst the Lepidoptera it 
is not remarkable. In the Hymenoptera Order it is 
mostly represented, I think, by a double ridge or fork, 
sometimes however obsolete, but very conspicuous in the 
saw-flies, which laterally terminates the postdorsolum ; 
the upper branch, usually the thickest, going to the an- 
terior part of the base of the underwing, and the lower 
one to the posterior. You may observe something simi- 
Jar in the crane-flies (Tipula) and Asilide. A tendon 
proceeding from the point of the postscutellum forms a 
fork near its end, the upper branch of which connects 
with the anterior and the lower with the posterior valve 
of the winglet; the structure is a little, but not essenti- 
ally, different in other Diptera. 
12, Pleura’. By this name I would distinguish the 
part which laterally connects the metathorax and post- 
pectus. It includes in it the socket of the secondary 
wings. In the Coleoptera this is a two-sided piece lying 
between the postfrenum and the parapleura, with the 
upper side horizontal and the lower vertical*—a tendon 
usually proceeds from its anterior extremity to the base 
of the wing. In the Orthoptera, Neuroptera, and other 
Orders, it is merely the longitudinal line of attachment 
of that part ; but in the genus Belostoma, related to the 
water-scorpion, it presents a peculiar structure, being a 
deep channel or demitube, filled at its posterior ex- 
tremity by a spiracle and its appendages *. 
* Prare VIII. Fie. 3. w'. » Prate XXII. Fic, 14. w’. 
© PLATE XXX, Fic, 95. w'. 
