TYPES OF CEPHALOPODA. 375 



though it may point forwards when the animal propels itself 

 through the water. Except in the Pearly Nautilus, the shell 

 of modern forms has been enclosed by the mantle, and is, in 

 most cases, only hinted at. There is a very distinct head 

 region, furnished with eyes and other sensitive structures, and 

 the mouth has strong beak-like jaws, as also a well developed 

 radula. The nervous system shows considerable specialisation, 

 and the chief ganglia are concentrated in the head. The true 

 body cavity, pericardium of other Molluscs, is usually well 

 developed, and frequently surrounds the chief organs. Except 

 in Nautilus, /"/ communicates with the exterior by the nephridia. 

 The vascular system is well developed, and, except in 

 Nautilus, there are accessory branchial hearts. The sexes are 

 separate. Development is direct. In habit, Cephalopods are 

 predominantly active and predatory ; in diet, carnivorous. 



TYPES OF CEPHALOPODA. 

 First Type. The Common CUTTLEFISH (Sepia officinalis). 



Mode of Life. 



This common cuttlefish is widely distributed, especially 

 in warmer seas like the Mediterranean. Unlike the Octopus, 

 which usually lurks passively, the Sepia is an active swimmer; 

 it moves head foremost by working the fins which fringe 

 the body, or it jerks itself energetically backwards by the 

 outgush of water through the funnel. It likes the light, and 

 is sometimes attracted by lanterns. The beautiful colours 

 change according to external conditions and internal emo- 

 tions ; and a plentiful discharge of ink often covers its retreat 

 from an enemy. Its food includes fish, other molluscs, and 

 crabs. In spring the female attaches her encapsuled eggs 

 to sea weeds and other objects, and often comes fatally near 

 the shore in so doing. The " cuttles " are caught for food 

 and bait. The " cuttle bone " and the pigment of the ink 

 bag are sometimes utilised by man. 



External Appearance. 



A large Sepia measures about 10 inches in length and 

 4 to 5 in breadth ; the body, fringed by a fin, is shaped like 

 a shield, the broad end of which bears a narrower head, 



