INTERNAL ANATOMY OF INSECTS. 97 
of nutriment; while their shortness and slenderness in- 
dicate that the insect lives by prey?. 
In considering therefore the parts connected with the 
digestive functions of the insect world, it will not be amiss 
to have reference to their food, and their mode of taking 
it; but first it will be proper to state and define the parts 
of this important organ. 
In general the alimentary canal’ is composed of the 
same essential tunzcks as that of the vertebrate animals, 
consisting of an interior epidermis, a papillary and cellu- 
lar tunick, and an exterior muscular one‘. ‘The first is 
usually tender, smooth, and transparent; but not always 
discoverable, probably on account of its tender sub- 
stance*?. Ramdohr does not notice the papillary and 
cellular tunicks; they are probably synonymous with what 
he denominates—the flochky layer (Die flockige lage), and 
which he describes, when highly magnified, as appear- 
ing to consist of very minute globules or dark points, and 
as being of a cellular structure*. The exterior tunick is 
thicker and stronger than the zntertor, and composed of 
muscular fibres, running either longitudinally or trans- 
versely, so as to form rings round the canal. This tu- 
nick mostly begins at the mouth, and goes to the anus, 
changing its conformation in different parts of the 
above intestine. Sometimes however it originates only 
at the beginning of the stomach‘. With respect to its 
general disposition, that canal—in its relative length, in 
the size of its different parts, in the number and form of 
its dilatations, and particularly of its stomachs and its 
2 Cuv. Anat. Comp. iv. 129. > Prate XXI. Fie..c, d,e, is the 
intestinal canal of the larva.of the Cossus. ‘° Cuv. Ibid. 112. 
4 Ramdohr Anat. der Ins. 6. © Thid. 25. ££ Ibid. 6. 
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