COMPARATIVE ANATOMY. 
the jaws are very large and manifest, and 
often possess denticulated edges. All the 
genera of the following orders have jaws j 
«fe. the coleoptera, orthoptera, neuroptera, 
and hymenoptera. The insects of the re- 
maining orders derive their nourishment 
chiefly from liquids ; which they get either 
from animal or vegetable substances by 
means of a spiral and tubular tongue, or a 
soft proboscis, as in the lepidoptera ; witli a 
broad opening, admitting of extention and 
retraction (the hemiptera); or a horny point- 
ed tube, containing sharp bristly bodies in- 
ternally (the diptera and aptera). 
The stomach of the bee is a transparent 
membranous bag, in which the nectar of 
the flowers is elaboi'ated and converted into 
honey. The animal vomits it up from this 
reservoir, and deposits it in the hive. 
The stomach of the crab and lobster is a 
very singular organ. It is formed on a bony 
apparatus, in short a species of skeleton, 
and does not therefore collapse when empty. 
To certain parts of this bony structure, 
round the pylorus, the teeth are affixed. 
Their substance is extremely hard, and their 
margin is serrated or denticulated ; as they 
surround the tube, near the pylorus, nothing 
can pass that opening without being per- 
fectly comminuted. These bones and teeth 
are moved by peculiar muscles. 
In thos-e mollusca, which possess jaws, 
these parts are fixed in the flesh of the ani- 
mal, as there is no head to which they can 
be articulated. They are two in number in 
the cuttle-fish, are composed of a horny 
substance, and resemble exactly the bill of 
a parrot. They are placed in the centre of 
the lower part of the body, and are sur- 
rounded by the tentacula, which enable the 
animal to attach itself to any objects. By 
means of these parts, the shell-fish, which 
are taken for food, are completely triturat- 
ed. The common snail and slug have a 
single jaw semilunar in its form, and den- 
ticulated. The tritonia has two jaws which 
act like the blades of a pair of scissars. 
The otlier mollusca possess no organs of 
this kind, but have, in some instances, a 
sort of proboscis ; as the buccinum, mut ex, 
voluta, doris, scyllsea, &c. 
In the worms, properly so called, there 
are sometimes hard parts forming a kind of 
jaws or teeth ; thus, in the nereis, the mouth 
possesses several calcareous pieces. The 
aphrodite (sea-mouse) has a proboscis, fur- 
nished with four teeth, which it can extend 
and retract at pleasure. Within the mouth 
«f the leech are three semicircular project- 
ing bodies, with a sharp denticulated edge : 
by this apparatus the animal inflicts its 
wound of the w'ell known peculiar form in 
the skin. 
The teeth of the echinus (sea-hedgehog) 
are of a very singular arrangement ; a round 
opening is left in the shell for the entrance 
of the food ; a bony structure, on which 
five teeth are placed, fills up this aperture ; 
and as these parts are moved by numerous 
muscles, they form a very complete organ 
of mastication. 
The stomach of the vermes, is in general, 
a membranous bag, but in some cases its 
structure is more complicated. The helix 
stagnalisandthe onchidia have gizzards. The 
aplysia has three strong muscular stomachs, 
provided with pyramidal bony processes. 
The latter structures, together with those 
of the lobster and crab, present a new 
analogy, as Cuvier has observed, between 
the membranes of the intestines and the in- 
teguments of the body. This is particularly 
strengthened by the annual shedding of the 
lobsters teeth, when its crustaceoiis cover- 
ing falls off. 
The bulla lignaria has a very powerful 
stomach, containing three hard calcareous 
shells, by which the animal is enabled to 
bruise and masticate the'other testacea on 
which it feeds. 
ON THE INTESTINAL CANAL; 
The intestinal canal (which is the most 
common part in the whole animal kingdom 
after the stomach) is distinguished in the 
mammalia by two peculiarities, which de- 
pend on the mode of nutrition. It is com- 
paratively shorter in carnivorous animals, 
and there is also in these less difference to 
external appearance between the small and 
the large intestine than in the herbivora. 
Yet these rules are not without tlieir excep- 
tions ; for the seal has very lona^ and the 
sloth very short intestines; the badger, 
which is not a proper carnivorous animal; 
and several true herbivora, as, for instance; 
the rell- mouse (glis e.sculentus) have no dis- 
tinction between the large and small intes- 
tine, &c; 
In considering the proportionate lengths 
of the intestinal canal, and the relation 
which these bear to tiie kind of food on 
wtiidi the animal subsists, many circum- 
stances must be taken into the account be- 
sides the mere measure of the intestine. 
Valvular projections of the internal mem- 
brane ; dilatations of particular parts of the 
canal ; and a large general diameter, com- 
