530 EXTERNAL ANATOMY OF INSECTS. 
Linné, or the upper side of the trunk, is resolvable; and 
those of the breast I denominate antepectus, medipectus, 
and postpectus. If terms be thought necessary to de- 
signate the two intire segments into which the alitrunk 
is resolvable, the first may be the meditrunk (medi- 
truncus), and the other the potrunk (potruncus). 
I. Substance.— With regard to its substance, the trunk 
in general is softer than the head, and harder than the 
abdomen, especially as to its upper surface; but in some 
cases, where it is not protected by the elytra, as in the 
rove-beetles (Staphylinus, &c.), the abdomen appears as 
hard as the trunk. Though usually not very different 
from the elytra in this respect, in Meloe, Cantharis, and 
other vesicatory beetles, it is of a firmer consistence. 
II. General Form.—In the Coleoptera Order the only 
part of the trunk that is visible on its upper-side is the 
prothorax: the mesothoraz, with the exception of the 
scutellum, and the metathorax, being entirely concealed 
by it and the elytra; so that, with regard to shape, it 
may nearly be considered as merging in the prothoraz. 
Below it is more visible, and may be stated as more or 
less quadrangular ; in oblong beetles inclining to a pa- 
rallelogram, and in shorter or hemispherical ones to a 
square. In the majority it is more convex below than 
above, except in the case of the hemispherical or gibbous 
beetles (Coccinella, Erotylus, &c.), in which the under- 
side is flat and the upper-side very convex. In the 
Diurnal Lepidoptera the trunk approaches to a cubical 
shape, in the Nocturnal it is more spherical. <A similar 
difference obtains in the Hymenoptera and Diptera: in 
