6 MANUAL OF THE MOLLUSCA. 



Chapter II. 



CLASSES OE THE MOLLUSCA. 



The mollusca are animals with soft bodies, enveloped in a mns- 

 culai- skin, and usually protected by a univalve or bivalve shell. 

 That part of their integument which contains the viscera and 

 secretes the shell, is termed the mantle ; in the univalves it 

 takes the form of a sac, with an opening in front, from which 

 the head and locomotive organs project : in the bivalves it is 

 divided into two lobes. 



The univalve mollusca are eiicQpJialous, or furnished with a 

 distinct head ; they have eyes and tentacula, and the mouth is 

 armed with jaws. Cuvier has divided them into three classes, 

 founded on the modifications of theii' feet, or principal locomo- 

 tive organs. 



1. The cuttle-fishes constitute the first-class, and are termed 

 cephalopoda,'^ because their feet, or more properly arms, are at- 

 tached to the head, forminor a circle round the mouth. 



Fig. l.f Oral aspect of a Cephalopod. 



* From Cephale, the head wApoda feet. Seethe frontispiece and pi. I. 



t Fig, 1. LoVigo vulgaris, Lam. \. From a specimen taken off Tenby, by J. 

 S. Bowerbank, Esq. The mandibles are seen in th&centre, surrounded by the 

 circular lip, the buccal membrane (with two rows of small cups on its lobes), 

 the eight sessile arms, and the long pedunculated tentacles (t), with their en- 

 larged extremities or clubs (c). The dorsal ai'ms are lettered (d), the funnel (f). 



