CEPHALOPODA DIBRANCHIATA. 



At the head of the Mollusca are the Cuttle-fishes, 

 animals whose aspect and actions remind us of Vertebrata, 

 and whose structure indicates a high type of organization 

 as compared with those of other molluscous tribes. These 

 remarkable mollusks are distinguished from their gastero- 

 podous relatives externally by the position and shape of 

 their principal prehensile and locomotive organs ; these are 

 arm-like processes springing from the head, and surrounding 

 the mouth, which is armed with powerful jaws resembling 

 the bill of a bird. The so-called mantle is a sleeve-like 

 investment of the visceral sac, and in certain tribes, now 

 for the most part extinct, was protected by a shell often of 

 singularly complicated structure. The head is strengthened 

 by a cartilaginous skeleton, which serves to protect the 

 highly-concentrated cephalic ganglions. The organs of 

 sense are highly developed. The gills are symmetrically 

 arranged plumes, lodged in a cavity which opens beneath, 

 with a fleshy siphonal tube springing from the back of the 

 neck at its orifice. The sexes are separate. All Cuttle- 

 fishes inhabit the sea. 



These animals play such an unimportant part in the fauna 

 of the British seas, that we should scarcely be warranted 

 in discussing at length the numerous questions of interest 

 connected with the class. Those that now live on our coasts 

 are members of the Dibranchiate order ; a group charac- 

 terised by the development of a distinct head provided 

 with sessile though conspicuous eyes, horny jaws, acetabu- 

 liferous arms, two branchial plumes, an ink-gland, a com- 

 plete siphon, and a shell which is very rarely external, 

 usually internal and penshaped. 



