EXTERNAL ANATOMY OF INSECTS. 353 
greater sections—the Head, the Trunk, and the Limbs. 
That of insects, likewise, is resolvable into three primary 
sections, but without including the limbs (which, as be- 
ing appendages, and therefore secondary, had best be 
considered under the section of which they form a part), 
for the abdomen in insects, as well as the rest of the body, 
being covered with a crust, and forming a distinct part, 
may be properly regarded as a primary section. And in 
fact these three parts may be received as primary under 
another view—the head, as containing the principal or- 
gans of sensation ; the trunk, as containing those of mo- 
tion; and the abdomen, as containing those of genera- 
tion*, Under each of these primary sections, I shall 
consider its respective organs, members, and parts. 
You are not to expect to find every part included in 
the following Table in every insect; since it has been my 
aim to introduce into it, the most remarkable of those 
that are peculiar to particular tribes, genera, &c. With 
respect to these, I shall generally refer you to the indi- 
viduals in which they may be found. 
DEFINITIONS. 
Corpus (the Body). The whole crust of the insect ; 
consisting of the Ezoderma or external covering, and 
the Hsoderma or internal cuticle that lines it. It is 
divided into three primary parts, or sections—Caput, 
Truncus, Abdomen. 
* See above, p. 28—. 
» The crust which covers the body of insects is lined internally 
with a kind of fibrous cuticle. Query, Whether in any degree ana- 
logous to the Periosteuwm of Vertebrate animals ? 
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