EXTERNAL ANATOMY OF INSECTS. 593 
female moths, in Cryptus hemipterus a Hymenopterous 
insect, &c. 
iii. Composition. The structure of wings has been 
before explained to you*, and I shall again have occa- 
sion to allude to it; but here I wish to call your attention 
to a circumstance that has not hitherto, that I recollect, 
been adverted to; I mean that all kinds of organs of 
flight, and it may be traced as we shall soon see even in 
elytra, are divided longitudinally into three areas or folds; 
the first or external one I call the Costal Area> from its 
beginning with the costal nervure ; the second is the Jn- 
termediate Area‘; and the third is the Anal Area, 
Having made these observations with respect to the 
organs of flight in general, I shall now proceed to consider 
more at large the elytra, tegmina, hemelytra, and wings. 
i. Elytrae. These are the wing-covers of the Coleo- 
ptera Order, distinguished from tegmina by the absence 
of nervures, from hemelytra by the want of the membrane 
at the apex, and from both by their uniting in almost 
every instance at the suture. I shall consider them as 
to their substance ; articulation with the trunk ; expan- 
sion ; parts; shape; appendages ; sculpture ; clothing ; 
colours, and uses. 
1. Substance. The firmness of the substance of elytra 
is usually regulated by that of the crust of the insect to 
which they belong; in hard insects they are hard, and 
* Vor. IT. p. 342—. b Prares X. and XXVIII. &. 
© Thid. c*. 4 Ibid. d:. 
© Oken (Carus Introd. to Comparat. Anat. i. 104. Engl. Tr.) sees 
an analogy between elytra and bivalve shells ; but this seems rather 
fanciful. 
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