STRUCTURE OF SEPIA. 



333 



change, and the beauty is enhanced by numerous " irido- 

 cysts " or modified connective tissue cells, with fine markings 

 which cause iridescence. 



The Muscular System. — The cuttlefish is very muscular, 

 notably about the arms, the mantle flap, and the jaws. 

 With great quickness it 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 con- 

 tract, 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. In rapid succession 

 gush follows gush, but all silently, though you may hear the 

 Sepia " blow " when it is removed from the water and gives 

 a final mantle gasp in air. Another muscular development 

 is hardly less interesting, that of the suckers on the arms. 

 They are muscular cups, borne on little stalks (unstalked in 

 Octopus, etc.), 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 bears small 

 chitinous teeth. Each cup acts as a sucker, in a fashion 

 which has many analogues, by increasing the size of the 

 cavity after the margin has been applied to some object or 

 other. The external pressure is then greater than that 

 Vithin the cup, and the little teeth keep the attachment 

 from slipping. 



Skeletal System. — An internal skeleton, a new item of 

 structure, is represented by supporting cartilaginous plates in 

 various parts of the body, especially (a) in the head, round 

 about the brain, arching over the eyes, enclosing the "ears" ; 

 (6) at the bases of the arms ; {c) as a crescent on the neck ; 

 (d) at the hook-and-eye arrangemerit 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 as a relic of its bearer, the 

 " cuttle-bone " or sepiostaire, and one sees it often in the 

 windows of bird-dealers' shops. It is given to cage-birds to 



