STRUCTURE OF SEPIA 46 1 



close to the pedal ganglia. The nerves seem to come from the pedals, 

 but it is said that their fibres can be traced up to the cerebrals. 



A ciliated " olfactory sac " lies behind each eye, and is innervated 

 from a special ganglion near the optic. There are no osphradia of the 

 usual type. 



Finally, there are tactile or otherwise sensitive cells on various parts 

 of the body, especially about the arms. 



Apart from sight altogether, an octopus can find a dead fish at a 

 distance of over a yard in a few minutes, and even slight movements in 

 the water are detected. 



In many Decapods there are luminous organs, usually on the ventral 

 surface in diverse positions, and often buried. They may serve as 

 recognition-marks or as search-lights. They may be glandular or 

 non-glandular, and those of the second type are often somewhat 

 eye-like, with pigment layer, reflector, lens, and diaphragm, or with 

 some of these structures. Often, however, the luminescence seems to 

 be due to the activity of symbiotic bacteria. 



Alimentary system. — The cuttlefish eats food which 

 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 headwards 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 

 annexes. 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, " pyloric 

 sac," and intestine meet ; and thes^ ducts are fringed by 

 numerous vascular and glandular appendages, which are 

 called " pancreatic," and arise from the wall of the un- 

 paired portion of the nephridia. 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, paralys- 



