EXTERNAL ANATOMY OF INSECTS. 559 
of a spiral thread, or rather of a number of cartilaginous 
rings connected by elastic membrane ?, and consequently 
is capable of considerable tension and relaxation, as the 
tegmen rises and falls in flight. In the Lepidoptera it 
appears to be a short piece overhung by the scutellum, 
which as it approaches the base of the wing is dilated. 
In the Lidellulina, to go to the Neuroptera, it has the 
same kind of elastic nervure connected with the Anal 
Area of the wing which I have just described in the 
Homopterous Hemzptera ; another nervure, in Ashna 
at least, appears to diverge upwards from the scutellar 
angle to the Intermediate Area>: a structure little dif- 
ferent distinguishes the rest of the Neuroptera, and even 
the Trichoptera. In the Hymenoptera this part varies 
somewhat; in the majority perhaps of the Order, as well 
as in the Diptera, it appears to be merely the lateral ter- 
mination of the scutellum where it joins the wing; but 
in some tribes, as in the saw-flies (especially Perga), 
Sirex L., and the Ichneumonidae, a ridge, and sometimes 
two, runs from the scutellum to the wing ; the upper one, 
where there are two, as in Perga, being the stoutest, and 
connecting with the Costal Area, and the lower one with 
the Anal. 
5. Pnystega*®. We learn from M. Chabrier, that in 
the common dragon-fly, a space, consisting of three 
triangles, which immediately succeeds the frenum, af- 
fords attachment to no muscles, but merely covers aérial 
vesicles*. This is the part I have called the pnystega *. 
An analogous piece may be discovered in Phasma and 
a Prate XXVIII. Fie. 11.7. 
b’ Chabrier Sur le Vol des Ins. c. iii. t. viii—v. B. 7. 
© Prate IX. Fic. 7. m’. 4 Chabrier Sur le Vol des Ins. ¢, iii. 354, 
¢ From zvyus te breathe, and séye to cover. 
