) 
28: MOLLUSCA.—CLASS V. CEPHALOPODA. 
living remnant, which has proved that the vast assemblage of organic 
remains abounding in our secondary formations must have belonged to 
animals who once dwelt in full activity and vigour at the bottom of the 
ocean, constructing a discoidal shell by force of gravity, and hermetically 
sealing the vacated portion as they increased in bulk, to give them buoy- 
ancy under the surrounding pressure. 
The body of the Cephalopodous mollusks presents exactly the appear- 
ance of an ovate or oblong bag; the viscera, or abdominal portion of the 
animal, being contained in a strong muscular bag-like mantle ; and it is 
often furnished either posteriorly or laterally with a pair of fin-like pro- 
cesses to assist locomotion. The head, which is situated at the opening 
of this bag, is provided with a vivid pair of eyes, as also with a strong 
pair of horny mandibles like the beak of a parrot, and it is crowned with 
a number of long active tentacles, which, being armed with suckers, per- 
form the several offices of crawling, swimming, and preying. The suck- 
ers possessing a strong power of attachment, are either sessile or pedun- 
culated, and in the latter case assume the terrific character of claws. 
The respiratory functions are performed either by two or four somewhat 
foliated branchiz ; the water is inhaled at the pallial aperture, and passes 
out by the excretory funnel or vent-tube, which protrudes from the front 
of the neck. The sexes are separate, and the females, which are consider- 
ably the more abundant as far as can at present be ascertained, deposit 
an enormous quantity of eggs. They are all provided with a capacious 
ovary at the posterior extremity of the mantle; some discharge their 
eggs in strings upon the rocks, whilst others construct a light, papy- 
raceous shell, for protecting them when impregnated. 
Very few of the Cephalopods are conchiferous; and in only one of 
these instances, in Nautilus, does the shell appear designed for the com- 
plete envelope of its inhabitant. The light papyraceous shell of the Ar- 
gonaut seems merely a sexual provision in the female for the preservation 
of her eggs; it is modelled on a different type from that of other mol- 
lusks, being secreted from the outside by two of the tentacles, which pos- 
sess a feeble power of calcification. Many of the naked Cephalopods have 
a kind of cartilaginous plate, the analogue of a shell, inserted within the 
