OF DIGESTION. 370 



therefore, compares this caecum of the Lepidoptera to the urinary 

 bladder, and it would we were to institute an analogy with the birds, 

 be analogous to the bitrsa Fabricn of those animals. Thus much is 

 certain, that this caecum cannot be of so much importance to digestion 

 as, for example, the caecum of the Rodentia, or the clavate and thick 

 intestine of other insects which are analogous organs. 



The true rejecting portion of the intestinal canal is therefore the 

 colon. By its considerable size, in the majority of cases, it is adapted 

 to the reception of much matter, and peculiarly adapted, by its strong 

 muscular structure, to the compression of it into lumps of excrement. 

 To promote this object, it has in many cases hard horny ridges and 

 prominences, which assist it in its function. The shape of the ex- 

 crement depends both upon the size of the colon and its folds. It is so 

 various in the caterpillars of the Lepidoptera, that frequently, with a 

 little attention, distinct genera and species may be distinguished by it, 

 a skill which is not unimportant to those who have the care of planta- 

 tions. In general, vegetable-feeding insects produce more excrement 

 than the carnivorous ones. This is distinctly shown in the caterpillars 

 and grasshoppers, the short but broad colon of which exclude at 

 intervals of a few minutes considerable balls of excrement,, which are 

 shaped precisely according to its form. In general, the digestion of 

 these insects is so rapid, that the just filled intestinal canal will have 

 extracted all the chyle in the course of one hour, and the caterpillar 

 recommence eating. Indeed, the food passes through the entire intes- 

 tine merely to make room for constantly succeeding food, and a voracious 

 caterpillar, therefore, will be continually evacuating excrement. In 

 the perfect insect, the colon is wider than the rest of the intestine, 

 but towards the anus it again contracts, and it consequently evacuates 

 the excrement in smaller, at least thinner, portions, or in a more fluid, 

 thick, pappy consistency ; haustellate insects, such as the Lepidoptera 

 and flies, reject it quite liquid. The colour of the excrement also 

 depends upon the difference of food ; for instance, that of the cockchafer 

 is green, like the leaf of the plant upon which it feeds ; that of the 

 water beetle of a yellow white, like the flesh he has eaten ; that of the 

 flea red, like the blood it has imbibed ; yet the colour always changes 

 a little ; it becomes, namely, darker, brownish or blackish, as in the 

 flies, which lap so many different kinds of nutriment. No peculiar 

 offensive or stinking smell is observed in the excrement of insects, and, 

 indeed, their rapid digestion does not admit of so complete a decom- 



