(51 ) 
their shape is sometimes that of a leaf, and sometimes it is similar to a sword 
blade. Their connection with the soft parts is the same as the bone of the 
Cuttle-fish. 
We also find a small semi-corneous and semi-friable plate in the body of 
the fleshy lobe which covers the branchize of the Aplysia, and there is one 
still smaller inthe cloak of the Slug. 
Every thing tends to convince us that those hard parts which are found 
within Mollusca, grow by strata, like their external envelope, and that they 
are a kind of internal shells. : 
Mottusca. Cuvier. (4) 
Without vertebrz or articulated members ; with blood vessels and nerves (2) ; 
a simple spmal marrow; lymph, chyle and blood of the same color (a bluish 
white) ; generally with salivary glands; a voluminous liver furnishing a great 
quantity of bile ; no pancreas or mesentery ; muscles (3) attached to the skin, 
which forms a soft envelope, contractile, engendering (in several species) 
stony plates or shells; the viscera and nervous system within this envelope, 
the latter composed of scattered masses united by nervous filaments, the 
principal of which, placed on the cesophagus, are called the brain; a coms 
plete system of circulation; respiratory organs; organs of digestion and se- 
cretion almost as complicated as in yertebrated animals (4). 
(1) Before Cuvier, naturalists divided all the invertebral animals into two classes, 
Insects and Worms. 
(2) Humboldt has adopted an ingenious method of distinguishing the nerves 
from the arteries, or other parts, in the smallest animals. He uses two needles, one 
gold, the other silver : a point of one is applied to the muscles, and a point of the 
other to the filament, the nature of which he wishes to discover, while the other 
extremities of these instruments are brought in cuntact. If the filament bea nerve, 
contractions immediately take place in the muscular fibre. 
(3) The Mollusca with an exterior shell, as Helices, Bulimi, Volutz, etc. have but 
one muscle which attaches their body to the shell, by a small part of the back and 
nearly in the middle of its length. This muscle forms a considerable tendon, 
similar to a thin ribband, which divides itself into two or three principal ribbands. 
Each of these subdivides itself into several smaller, which disperse and distribute 
themselves into all parts of the body. The Mollusca witha univalve shell furnished 
with an operculum, have two muscles of attachment : one of these muscles unites 
the animal to its shell and resembles that just described in the univalves without 
opercula; the other, which adheres to the operculum, is generally round, very 
wide, but not thick. 
(4) The Mollusca with a trunk, as the Buccini, Volutaw, etc. are carnivorous ; 
they make use of their trunk asa gimblet, and even bore through other shells and 
suck the flesh of the animals within. Those which have strong horny jaws and a 
beak like a parrot, are also carnivorous or nourish themselves with animal sub- 
stances, like the Cephalopoda. The Mollusca which have a muffle and two jaws, 
one of which at least is furnished with small teeth, are herbivorous or frugivorous, 
such as the Limaces, Helices, Bulimi, etc. 
. 
