CUTTLEFISH. 403 



within the mantle cavity lie the anus and the openings of 

 the nephridia and genital duct. 



The true orientation of the different regions in Sepia is 

 not obvious. If the <r arms " surrounding the mouth be 

 divided portions of the anterior part of the "foot," the 

 - ventral surface is that on which the animal rests when we 

 make it stand on its head. We can fancy how the "foot" 

 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 tissue 

 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. 



