CEPHALOPODA. ee is17/ 
secretion of an inky fluid, with which to cloud the water and 
conceal retreat ; more perfect organs of vision; and superadded 
branchial hearts, which render the circulation more vigorous. 
The suckers (antlia or acetabula) form a single or double series 
on the inner surface of the arms. From the margin of each 
cup, the muscular fibres converge to the centre, where they 
leave a circular cavity, occupied by a soft caruncle, rising from 
it like the piston of a syringe, and capable of retraction when 
the sucker is applied to any surface. So perfect is this mechanism 
for effecting adhesion, that while the muscular fibres continue 
retracted, it is easier to tear away the limb than to detach it 
from its hold.* In the decapods, the base of the piston is sur- 
rounded by a horny dentated hoop; which in the uncinated 
calamaries is folded, and produced into a long sharp claw. 
The ink-bag (Fig. 40) is tough and fibrous, with a thinsil very 
outer coat; it discharges its contents through a duct which 
opens near the base of the funnel. The ink was formerly used 
for writing (Cicero), and in the preparation of sepia,+ and from 
its indestructible nature, 1s often found in a fossil state. 
The skin of the naked cephalopods is remarkable for its 
variously coloured vesicles, or pigment-cells. In sepia they 
are black and brown; in the calamary, yellow, red, and brown ; 
and in the argonaut, and some octopods, there are blue cells 
besides. These cells alternately contract and expand, by which 
the colouring matter is condensed or dispersed, or perhaps 
driven into the deeper part of the skin. The colour accumulates, 
like a blush, when the skin is irritated, even several hours after 
separation from the body. During life these changes are under 
the control of the animal, and give it the power of changing its 
hue, like the chameleon. In fresh specimens, the sclerotic plates 
of the eyes have a pearly lustre; they are sometimes preserved 
in a fossil state. 
The aquiferous pores are situated on the back and sides of the 
head, on the arms (brachial), or at their bases (buccal pores). 
The mantle is usually connected with the back of the head by 
a broad (‘‘ nuchal’’) muscular band; but its margin is some- 
* «The complex, irritable mechanism of all these suckers is under the complete 
control of the animal. Mr. Broderip informs me that he has attempted, with a hand- 
net, to catch an octopus that was floating by, with its long and flexible arms entwined 
round a fish, which it was tearing with its sharp hawk’s bill; it allowed the net te 
approach within a short distance before it relinquished its prey, when, in an instant, it 
relaxed its thousand suckers, exploded its inky ammunition, and rapidly retreated, 
under cover of the cloud which it had occasioned, by rapid and vigorous strokes of 1ta 
circular web.”— Owen. 
¢ Indian ink and sepia are now made of lamp-smoke, or of prepared charcont, 
