STRUCTURE OF SEPIA 457 



of a snail might grow forward and surround the mouth, so 

 as to bring that into the middle of the sole. Then the 

 visceral mass has been elongated in an oblique dorso- 

 posterior direction, so that the tip of the shield, directed 

 forward when the cuttle jerks itself away from us, represents 

 in anatomical strictness the dorsal surface tilted backwards. 

 (As above noticed, the animal may also swim with foot and 

 mouth in front.) The side of lighter colour, marked by the 

 mantle cavity and the siphon or funnel, is posterior and 

 slightly ventral ; the banded and more convex side, on 

 which the cerebral ganglia lie in the head region, and on 

 which the shell lies concealed in the visceral region, is 

 anterior and slightly dorsal. 



Skin. — There are numerous actively changeful pigment 

 cells or chromatophores lying in the connective tissme 

 beneath the epidermis. Each cell is expanded by the 

 contraction of muscular cells which radiate from it, and 

 contracts when these relax. It is probable that these 

 chromatophore cells have some protoplasmic spontaneity 

 of their own, but the controlling muscular elements are 

 also affected by nervous impulses from the central ganglia. 

 As the cells dilate or contract, the pigment is diffused or 

 concentrated, and the colours change. The animal's 

 beauty is further enhanced by numerous " iridocysts " or 

 modified connective tissue cells, with fine markings which 

 cause iridescence. 



Muscular system. — The cuttlefish is very muscular, 

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

 Many of the muscles show double oblique striping. The 

 animal 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 arrange- 

 ment ; 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. The suckers on the 

 arms are muscular cups, borne on little stalks (unstalked 



