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MANUAL OF ZOOLOGY. 



shaped cavity, the muscular fibres of which converge to the 

 centre, where there is a little muscular eminence or papilla. 



When the sucker is applied to 

 any surface, the contraction of the 

 radiating muscular fibres depresses 

 the papilla so as to produce a 

 vacuum below it, and in this way 

 each sucker acts most efficiently 

 as an adhesive organ. In some 

 forms (Decapoda) the base of the 

 papilla, or piston, is surrounded 

 by a horny dentated ring, and in 

 some others (as in Onychoteuthis] 

 the papillae are produced into 

 long claws. In the Octopod 

 Cuttle-fishes there are only eight 

 arms, and these are all nearly 

 alike. In the Decapod Cuttle- 

 fishes there are ten arms, but 

 two of these called " tentacles " 

 are much longer than the 

 others, and bear suckers only at 

 their extremities, which are en- 

 larged and club-shaped. In the 

 Nautilus the arms are 

 and are devoid of 

 suckers. 



The arms are really produced by an extension of the mar- 

 gins of the " foot," or of the part corresponding to the foot of 

 the other Mollusca. The " antero-lateral parts of each side of 

 the foot extend forwards beyond the head, uniting with it and 

 with one another; so that, at length, the mouth, from having 

 been situated, as usual, above the anterior margin of the foot, 

 comes to be placed in the midst of it. The two epipodia, on 

 the other hand, unite posteriorly above the foot, and where they 

 coalesce, give rise either to a folded muscular expansion, the 

 edges of which are simply in apposition, as in the Nautihis ; 

 or to an elongated flexible tube, the apex of which projects 

 beyond the margin of the mantle, called the 'funnel,' or 

 ' infundibulum/ as in the dibranchiate Cephalopoda" 

 (Huxley.) 



The mouth leads into a buccal cavity, containing two 

 powerful, horny or partially calcareous, mandibles, working 

 vertically like the beak of a bird ; together with an " odonto- 

 phore" or "tongue," the anterior part of which is sentient, 



Fig. 107. Cephalopoda. Sepiola Pearly 

 Atlantica, one of the Cuttle-fishes 

 (after Woodward). " UlTierOUS, 



