EXTERNAL ANATOMY OF INSECTS. 619 
haps in those minute Hymenoptera whose wings have 
solely the costal nervures; probably in these there is only 
one axis. In the Lepidoptera and Hymenoptera a cir- 
cumstance connected with the present head is observable, 
which is not to be discovered in the other Orders : these 
are the tegule or base-covers, which appear intended to 
defend the base of the anterior wings. ‘They are con- 
cavo-convex scales, which in the Lepidoptera are large 
and of an irregular shape*, but in the Hymenoptera are 
smaller and semicircular >. 
2. Wings, with regard to their substance, may generally 
be termed membranous; but they vary in this respect, 
some being much thicker than others, either partially 
or fotally: in spotted wings, as in those of many Libel- 
lulina, Cicade, &c., the dark opaque parts are denser 
than those that are transparent: in several Orthopterous 
insects, as in Phasma, some Mantes, &c., the Costal 
Area or covering part of the wing is of a substance 
equally firm with that of the fegmen. ‘This is a compen- 
sating contrivance, that where the latter is shorter and 
smaller than the former, its membranous part, when 
folded, may be protected from injury. Another similar 
contrivance of Diving Wispom is exhibited by those 
Pterophylla whose tegmina resemble the leaves of plants 
(Pt. laurifolia, &c.); in these the tip of the wings when 
folded being longer, is not covered by the tegmina, and 
therefore exposed to injury; to prevent which this small 
piece, while the whole wing, as far as covered by those 
organs, is membranous, is of the same substance with 
them‘. The wings of most Coleoptera, Orthoptera, 
Hemiptera, and Phasia subcoleoptrata, in the Diptera, 
a Prate IX, Fic. 5. » Ibid. Fic. 1]. 12, 2”. 
* Stoll Sauterelles d Sadr. t. iv. f. 12, t. vi. f. 21, &e. 
\ * 
