CEPHALOPODA. 63 



nished with muscular ventricles ; ink-gland always present ; parietes of the 

 funnel entire. 



Shell internal (except in argonauta), horny or shelly, with or without 

 air-chambers. 



The typical forms of the cuttle-fishes were well described by Aristotle, and 

 have been repeatedly examined by modern naturalists ; yet, until Professor 

 Owen demonstrated the existence of a second order of cephalopods, departing 

 from all the abovementioned characters, it was not clearly understood how 

 inseparably the organisation of the cuttle-fishes was connected with their con- 

 dition as swimming mollusca, breathing by two gills. 



The characters which co-exist with the two gills, are the internal ru- 

 dimentary shell, and the substitution of other means of escape and defence, 

 than those which an external shell would have afforded ; viz. : powerful arms, 

 furnished with suckers ; the secretion of an inky fluid, with which to cloud 

 the water and conceal retreat ; more perfect organs of vision ; and super- 

 added 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. Prom 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.f In the decapods, 

 the base of the piston is surrounded by a horny dentated hoop ; which in the 

 uncinated calamaries, is folded, and produced into a long sharp claw. 



The ink-bag (fig. 33), is tough and fibrous, with a thin silvery 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 pre- 

 paration of sepia ;% and from its indestructible nature, is often found in a 

 fossil state. 



* In a few species, which have no fins, the arms are webbed. In the only kind 

 which has an external shell, it is confined to the female sex, and is secreted by the 

 membranes of the arms. It is now quite certain that such shells as those of the fossil 

 ammonites and orthocerata. would be incompatible with dibranchiate organization. 



t " The complex, irritable mechanism, of all these suckers, is under the complete 

 control of the animal. Mr. Eroderip 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 to ap- 

 proach 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." (Owen.) 



J Indian ink and sepia are now made of lam :-smoke, or of prepared charcoal. 



