MANUAL OF THE MOLLUSCA. 



Chapter II. 



CLASSES OF THE MOLLUSCA. 



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

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

 That part of their integument which contains the viscera and 

 seci-etes the sheU, 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 encepJmlous, or furnished mth u 

 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 

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

 tached to the head, forming a cu-cle round the mouth. 



Fig. l.f Oral aspect of a Cephalopod. 



* From Cephale, the head and^o^^ feet. See the frontispiece aud pi. I. 



t Fig. 1. Loligo vulgaris, 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 arms, and the long pedunculated tentacles (t), with theu* en- 

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



