( 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 branchiae of the Aplysia, and there is one 

 still smaller in the 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. 



Mollusca. Cuvier. (1) 



Without vertebrae or articulated members ; with blood vessels and nerves (2) % 

 a simple spinal 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 oesophagus, are called the brain; a com- 

 plete system of circulation ; respiratory organs ; organs of digestion and se- 

 cretion almost as complicated as in vertebrated 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 contact. If the filament be a nerve, 

 contractions immediately take place in the muscular fibre. 



(3) The Mollusca with an exterior shell, as Helices, Bulimi, Voluta?, 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 with a 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, Volutoe, etc. are carnivorous • 

 they make use of their trunk as a 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 fru^ivorous* 

 such as the Limaces, Helices, Bulimi, etc. i 



2 



