3 6 ° 



MOLLUSC A. 



requires tearing and chewing, and this is effected by the 

 chitinous jaws worked by strong muscles, and by the 

 toothed radula moving on a muscular cushion. The mouth 

 lies in the midst of the arms, bordered by a circular lip, and 

 opens into a large pharynx or buccal cavity (cf. the snail). 

 The narrow gullet passes through the ganglionic mass, 



and leads into the globular 

 stomach, lying near the dorsal 

 end of the body. The stomach 

 is followed by a caecum or pyloric 

 sac, and the intestine curves head- 

 wards again, to end far forward 

 in the mantle cavity. There do 

 not seem to be any glands on 

 the walls of the food canal ; the 

 stomach has a hard cuticle ; the 

 digestion which takes place there 

 must therefore be due to the 

 digestive juices of the glandular 

 appendages. Of these the most 

 important is usually called the 

 liver; it is bilobed, and lies in 

 front of the stomach, attached to 

 the oesophagus. Its two ducts 

 conduct the digestive juice to the 

 region where the stomach, "py- 

 loric sac," and intestine meet; 

 and these ducts are fringed by 

 numerous vascular and glandular 

 appendages, which are called 

 "pancreatic,'' and arise from a 

 differentiated part of the digestive 

 gland. Far forward, in front of the 

 large digestive gland, lie two small white glands on each side 

 of the gullet, with ducts which open into the mouth (cf. the 

 " salivary glands " of the snail). A diastatic ferment has 

 been proved in the salivary secretion of Cephalopods, but 

 that of Octopus has a poisonous, paralysing effect on the 

 crabs, etc., which are bitten, and also a peptonising action. 

 At the other end of the food canal, the ink-sac, full of black 

 pigment, probably of the nature of waste products, opens 



of the 

 Mainly 



Fig. 156. — Diagram 

 structure of Sepia.— 

 after Pelseneer. 



i.,Eightshort arms around mouth ; 

 /.«., one of the two long arms ; 

 b. , beak of the mouth ; e.g. , cere- 

 bral ganglia, with commissures 

 to the others; E., eye; g., 

 gullet; d.g., digestive gland (the 

 "salivary glands" are not re- 

 presented) ; st., stomach ; a., 

 anus ; sk., shell-sac with sepio- 

 staire ; k., kidney ; R., Repro- 

 ductive organ ; br.h., branchial 

 heart ; g. t a gill ; i.b., ink-bag ; 

 m.c, mantle cavity ; /., funnel. 



