EXTERNAL ANATOMY OF INSECTS. 5$1 
the bees, wasps and flies, the trunk approaching to the 
figure of a sphere; in the ants, Scolie, crane-flies, &c. 
to that of a cube. The upper part of it in many Ichneu- 
monide, female ants, &c. is very elevated, forming an 
arch, and sloping towards the abdomen. In general it 
may be observed with respect to the remaining Orders, 
that the form of the trunk merges in that of the whole 
body, the tendency of which is often to a three-sided 
figure. 
III. Proportions.—The trunk is usually longer and 
larger than the head and longer than the abdomen, but 
not wider: but there are exceptions to both these rules. 
In Colliuris, Mantis, &c. itis more slender; and in Cico- 
doma cephalotes and some neuter ants, it is shorter than 
the head ; in Atractocerus, many Staphylinide, Phasma, 
the Libellulina, the Lepidoptera, and various Hymeno- 
ptera, it is shorter, and in the Mantide more slender 
than the abdomen. The greatest disproportion between 
it and the last part is exhibited by the genus Evania, 
parasitic upon the Blattina, in which the abdomen ap- 
pears merely as a minute and insignificant appendage 
of the trunk. The vertical diameter of this part, almost 
without exception, is greater than that of either head or 
abdomen. When we consider that it contains the mus- 
cles that move both the organs of flight and the legs, we 
see clearly the reason why the Creator gave it greater 
volume. 
IV. Composition.—I lately intimated to you that the 
trunk, though resolvable into three segments, in most 
cases properly consists of only #wo primary ones. Who- 
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