SEPIA. 377 



seizes its prey by throwing out its two long arms, which are 

 often entirely retracted within pouches. With great force it 

 jerks itself backwards by contracting the mantle cavity, and 

 making the water gush out through the pedal funnel. This 

 mode of locomotion is very quaint. At one time the mantle 

 cavity is wide, and you can thrust your fingers into its gape ; 

 when about to contract, this gape is closed by a strange 

 double hook and eye arrangement ; contraction occurs, and 

 the water, no longer free to leave as it entered, gushes out 

 by the funnel, the base of which is within the mantle cavity. 

 Another muscular development is interesting, that of the 

 suckers on the arms. They are muscular cups, borne on 

 little stalks (unstalked in Octopus, &c\ well innervated, and 

 able to grip with a tenacity which in the giant cuttlefishes 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 attachment from slipping. 



It seems likely that the arms represent a propodium, and 

 the siphon a mesopodium, and a valve within the siphon has 

 been compared to a metapodium. 



Skeletal System. 



An internal skeleton is represented by supporting cartila- 

 ginous plates in various parts of the body, especially (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 structureless transparent matrix of 

 the cartilage. 



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

 sepiostaire, which is sometimes given to cage birds to peck 

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

 on the dorsal 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 consists 



