CEPHALOPODA. 



61 



The stomach (Fig. 532 M) is usually spherical ; its walls are 

 muscular and its internal lining is raised into longitudinal folds or 

 papillae. It possesses a large, sometimes spirally wound, caecal 

 appendage, which opens into it close to the point of origin of the 

 intestine, rarely at some distance from that point. The ducts of the 

 large liver open into this caecum. A mass of yellow glandular lobes, 

 which are attached to the upper part of the bile ducts, may be in- 

 terpreted as pancreas (fig. 532 Gfg). The intestine is but little con- 

 voluted and the anus always opens in the middle line of the mantle 

 cavity. 



Jk Y L 



^^Siiss^^S:^ 



At 



FIG. 534. Horizontal section through the eye of Sepia (diagrammatic, after Hensen). KK, 

 cephalic cartilage ; C, cornea ; Z, lens ; Ci, ciliary body ; Jk, iris cartilage ; K, cartilage of 

 optic bulb ; Ae, argentea externa ; W, white body ; Opt, optic nerve ; Go, optic ganglion ; 

 Re, outer layer of rods, Ri, inner layer of rods of the retina ; P, pigment layer of the 

 retina. 



The nervous system is characterised by its great concentration 

 and high development. In the Dibranchiata the nerve centres 

 constitute a large ganglionic mass which is placed in the cartilaginous 

 cranial capsule and is perforated by the oasophagus (fig. 533). It is 

 divided into a dorsal and a ventral portion, connected by two com- 

 missures. The former corresponds to the brain (cerebral ganglia) 

 and sends nerves to the sense organs and to the buccal ganglia. The 

 ventral portion consists "mainly of the pedal and visceral ganglia. 



