342 



MOLLUSCA 



its secretion forms the basis of the well-known color, sepia. Nautilus 

 and some Octopoda have no ink sac. 



Just behind the buccal mass are the closely united chief ganglia of 

 the nervous system (fig. 357) surrounding the oesophagus. 



A single 



FIG. 356. Anatomy of Octopus vulgar is. T, basis of tentacles; K, head; M, 

 mantle split ventrally, opening visceral sac; liver and nephridia removed, venae cava? 

 with appendages folded back; a, anus; ao, aorta; au, eye; cv, vena cava with nephridial 

 appendage; d, intestine; e, pericardial sac with nephridial opening; go, optic ganglion; 

 h, systemic heart; z, crop (cesophageal appendage); k, gills; kh, branchial heart; kn, 

 cephalic cartilage; /, liver and /', gall duct (position of liver indicated by dotted line); 

 m, stomach; o, ovary; od, oviduct; />, pedal ganglion; r, passage connecting with ovary; 

 r', mouth of pericardial sac in nephridial sac; s, cesophagus with dorsal salivary gland; 

 s/>, ventral salivary glands; st, stellate ganglion; sv, sympathetic ganglion; /, ink sac; 

 v, visceral ganglion; rk, auricle of systemic heart; x, spiral blind sac. 



dorsal mass represents the cerebral ganglia; connected with this by 

 broad commissures, the pedal and visceral (viscero-pleuro-parietal) 

 ganglia lie close together ventrally. With these parts are associated 



