376 MOLLUSC A. 



with eight short and two long sucker-bearing arms. Besides 

 the diffuse pigment cells, there are bands across the " back." 

 The large eyes, the parrot-beak-like jaws protruding from 

 the mouth, the spout-like funnel on the neck, and the 

 mantle cavity are conspicuous. 



The true orientation of the different regions in Sepia is 

 not obvious. If the "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, '\^'e can fancy how the "foot" 

 of a snail might grow forward |ind surround the mouth, so 

 as to bring that into the micrdle 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. 



The Skin. 



The skin contains numerous actively changeful pigment 

 cells or chromatophores lying in the connective tissue 

 beneath the epidermis. Each cell is expanded by the 

 contraction of fine muscle fibres which radiate from it, and 

 contracts when the fibres relax. It is probable that these 

 chromatophore cells have some protoplasmic spontaneity of 

 their own, but the controlling fibres seem to be 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. With great quickness it 



