INTERNAL ANATOMY OF INSECTS. 125 
but in some species it is yellowish, or reddish, and its 
lower surface has sometimes regular excavations a ; no 
transverse hepatic ducts connecting it with the alimentary 
canal, as in the scorpion, appear to have been at present 
discovered : two pairs of capillary free vessels are at- 
tached to the base of the rectum on one side, which, ex- 
cept in their situation, seem analogous to the bile-vessels 
of insects b . 
From the above detailed account of the alimentary 
canal of the animals whose internal anatomy we are con- 
sidering, it appears that M. Cuvier's observation — that 
the length and complication of the intestines indicate a 
less substantial kind of nutriment — does not hold univer- 
sally: thus, in Necrophorus and Silpha, carnivorous insects, 
the intestinal canal in its length and convolutions exceeds 
those of most herbivorous ones, and in Cassida viridis and 
some others of the latter tribe are not longer than those 
of the predaccous beetles. In herbivorous larvae also, in 
general, the length of the alimentary canal does not ex- 
ceed that of the body, but in those of some Jlesh-dies 
(Musca vomitoria) it very greatly exceeds it c . So true 
is the observation — that there is no general rule without 
exceptions. 
In this letter it may not be out of place to say a few 
words upon the excrements of insects ; which, strange as 
the observation may seem, but it is no less true than 
strange, are sometimes pleasing to the eye, from their 
symmetry, and to the taste, from their sweetness. In 
those that masticate their food they are solid, and in 
those that take it by suction, fluid or semi-fluid. In the 
3 Treviran. Ibid. 28. b Ibid. I u.f. 24. ,3. 
c Ramdohr, /. six./. 1. 
