54 



CEPHALOPODA. 



fication of the mantle of the other MoUusca. Ordinarily 

 there is a tolerably distinct separation of the body (fig. 445) 

 into an anterior cephalic portion {iwosoma), and a posterior 

 portion, enveloped in the mantle, and containing the viscera 



{mctasoma). The liead is very 

 distinct, bearing a pair of large 

 globnlar eyes, and having the 

 mouth in its centre. The moutli 

 is surrounded by a circle of eight, 

 ten, or more, long muscular pro- 

 cesses or " arms " (fig. 445), which 

 are generally provided with rows 

 of suckers. In the Octopod Cuttle- 

 fishes there are only eight arms, 

 and tliese 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 ex- 

 tremities, which are enlarged and 

 club-shaped. In the Pearly Nau- 

 tilus the arms are numerous, and 

 are devoid of suckers. 



The parts of the Cq^halopoda 

 which may be preserved in a fossil condition, and which 

 thus interest the palaeontologist, are the mandibles, the ink- 

 hcKj, and the skeleton, whether this be internal or external. 



The mandiUes are contained within the mouth or "buccal 

 cavity " of the animal, and have tlie form of powerful jaws, 

 working vertically like the beak of a bird. They are 

 horny or sul3-calcareous, and in sliape closely resemble the 

 beak of a i»arrot, with this difference, that the largest of the 

 two mandibles is placed inferiorly. Mandibles of this 

 nature are present in both the Cuttle-fishes and the Pearly 

 Nautilus, being horny in the former and calcareous in the 

 latter, and they doubtless existed in all the extinct forms. 

 The calcareous beaks not uncommonly occur as fossils, but 

 they do not appear to have been observed out of tlie Juras- 



Fig. 445. — Cejihalopoda. Sepiola 

 AtUuitica, one of the Cuttle-fishes. 

 (After Woodward.) 



