CEFIIALOPODES. 337 



and incapable of active exertion, they maintain themselves amid living beings princi- 

 pally by their fecundity, and the tenacity with which they retain life. 



DIVISION OF THE MOLLUSCA INTO SIX CLASSES.* 



The general form of the body of the MoUusca being, in a sufficient degree, propor- 

 tional to the complication of their internal organization, indicates their natural divisions. 



In some, the body has the form of a sac, inclosing the branchiae, and open above, 

 whence there protrudes a head well developed, and crowned with certain strong fleshy 

 elongated productions, by means of which the animals progress, and seize upon objects. 

 We call these the Cephalopodes. 



In others, the body is not open ; the head has no appendages, or only very minute 

 ones ; the principal organs of locomotion are two wings, or membranous fins, placed 

 on the sides of the neck, and in which the branchial tissue is often spread. These are 

 the Pteropodes. 



Others, again, crawl on the belly on a fleshy disk, sometimes, though rarely, com- 

 pressed into a fin. They have almost all a distinct head. We call these the 

 Gasteropodes. 



A fourth class is composed of those Mollusca in which the mouth lies concealed in 

 the base of the cloak, which also incloses the branchiae and the viscera, and opens 

 either throughout its whole length, or at both its extremities, or at one only. These 

 are our Acephales. 



A fifth comprehends the species which, inclosed also in a cloak, and without an 

 apparent head, have fleshy or membranous arms, garnished with ciHae of the same 

 nature. We have called these the Brachiopodes. 



Lastly, there are some which, alike the other Mollusca in the cloak, the branchiae, 

 &c., differ from them in having numerous horny articulated members, and in a nervous 

 system more allied to that of the Annulose Animals. Of these we constitute our last 

 class, the Cirrhopodes. 



THE FIRST CLASS OF MOLLUSCA. 



THE CEPHALOPODES.* 



The cloak unites under the body, and forms a muscular sac, that incloses all the 

 viscera. In several species, its sides are extended into fleshy fins. The head issues 

 from the opening of the sac : it is roundish, furnished with two large eyes, and crowned 

 with fleshy conical arms or feet, varying in their length, and capable of being bent 

 very vigorously in every direction ; and, as their surface is armed with suckers, the 

 animals fix themselves, by their means, with great force to whatever objects they em- 

 brace. With their feet they seize their prey, walk, and swim. They swim w-ith the 

 head backwards, and crawl in all directions, with the head beneath and the body above. 



• For the name Molluscn, M. <ie Blainville proposes to substitute I classes is emirclj- my own, as well as the ifreater number of the sub 



Miilijcoznn; and he separates from them the Chitons and the Cirrho- I divisions to the second degree, 



pods, with which he makes a subtypical section nndrr the name I t The Ci-phrilnpfinra of f)e Blainville. 

 ifiiletitozoiiria. The following distribution of the Mollusca into | 



