CEPHALOPODA. 157 



Eecretion of an inky fluid, with whicli to cloud tiie 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-hag {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, is 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 (" wMc/iaZ ") 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 octopics that was floating by, with its long and flexible arms entwined 

 ronnd a fish, which it was tearing with its sharp hawk's bill ; it allowed the net to 

 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 its 

 circular web." — Oicen. 



t Indian ink and sepia are now made of lamp-smoke, or of prepared charcoal. 



