MANUAL OF THE MOLLUSCA. 



CHAPTER II. 

 CLASSES OP THE MOLLUSCA. 



THE mollusca are animals with soft bodies, enveloped in a mus- 

 cular 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 encephalous, or furnished with E 

 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 their 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, forming a circle round the mouth. 



Fig. l.f Oral aspect of a Cephalopod. 



* From Cepkale, the head and poda feet. See the frontispiece and pi. I. 



f Fig. 1. Loligo mdgaris, Lam. \. From a specimen taken off Tenby, by J. 

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

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

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

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



