4S8 



PHYLUM MOLLUSCA 



in Octopus^ etc.), well innervated, and able to grip with 

 a tenacity which in giant cuttlefish is dangerous even to 

 men. The inner edge of the cup margin is supported by 

 a chitinoid ring bearing small teeth. Each cup acts as a 

 sucker, in a fashion which has many analogues, for a 

 retractor muscle increases the size of the cavity after the 

 margin has been applied to some object. The external 

 pressure is then greater than that within the cup, and the 



little teeth keep the attach- 

 ment from slipping. 



It seems likely that the 

 arms represent a pro- 

 podium, and the siphon a 

 mesopodium, and a valve 

 within the siphon has been 

 compared to a metapodium. 

 Skeletal system. — An 

 internal skeleton is repre- 

 sented by supporting carti- 

 laginous plates in various 

 parts of the body, especi- 

 ally — (a) in the head, round 

 about the brain, arching 

 over the eyes, enclosing 

 the " ears " ; {b) at the 

 bases of the arms ; {c) as 

 a crescent on the neck ; 

 {d) at the hook-and-eye 

 arrangement of the mantle 

 flap ; {e) along the fringing 

 fins. Ramified " stellate " 

 cells lie in the structure- 

 less transparent matrix of the cartilage. 



On the shore one often finds the " cuttle bone " or sepio- 

 staire, which is sometimes given to cage birds to peck at 

 for lime, or used for polishing and other purposes. It lies 

 on the front side of the animal, covered over by the mantle 

 sac. In outline it is somewhat ellipsoidal, thinned at the 

 edges like a flint axe-head, and with curved markings which 

 indicate lines of growth. In the very young Sepia it con- 

 sists wholly of the organic basis conchiolin, but to this lime 



Fig. 259. 



External appearance of 

 a squid {Loligo). 



