XII 



PHYLUM MOLLUSCA 



763 



eye 



i... 



FIG. 0:36. Sepia cultrata, cranial car- 

 tilage seen from the posterior aspect, 

 with the cavities of the statocysts ex- 

 posed, eye, position of eye indicated by 

 dotted line ; of. statocyst ; pall. n. 

 pallial nerve ; rise. n. visceral nerves. 



nephridial aperture (neph.). On the left-hand side is the opening 

 of the sperm-duct or oviduct (ovid.) as the case may be. 



In addition to the shell, which is an important protective 

 structure, and gives support to the muscles of the fins, Sepia also 

 has a remarkably well developed internal skeleton composed of 

 cartilage. An important part of this the cranial cartilage (Fig. 

 656) protects the principal nerve- 

 centres, encloses the statocysts, 

 and gives support to the eyes. 

 Other cartilages support the bases 

 of the arms. A thin shield- 

 shaped plate the nuchal cartilage 

 (Fig. 657) lies on the posterior 

 surface of the neck. The pair of 

 elevations on the posterior wall 

 of the funnel and the correspond- 

 ing depressions on the anterior 

 surface of the body are borne 

 each on a thin plate of cartilage, 

 and other thin cartilages support 

 the bases of the fins. 



Alimentary System. - The 

 mouth is surrounded by a thin 



peristomial membrane, within which is a circular lip beset with 

 numerous minute elevations. Lodged within the circular lip is a 

 pair of powerful horny jaws (Fig. 659, Fig. 660, jaw 1 , jaw 2 ', Fig. 

 661, /. ; Fig. 663, jaw). These have somewhat the appearance of 

 the beak of a parrot, the posterior jaw being larger and more 

 strongly bent than the other, which it partly encloses. The mouth 



leads into a thick-walled buccal cavity, which 

 contains an odontophore bearing numerous minute 

 horny teeth. The cssophagus (Figs. 660 and 661, ce, ; 

 Fig. 663, 028), following on the buccal cavity, is a 

 narrow straight tube, which runs between the 

 halves of the " liver " towards the aboral end of the 

 body. It opens into a rounded thick-walled 

 stomach (st.), and, close to the pyloric aperture 

 leading from the latter into the intestine, opens 

 a wide case-urn (c.). The alimentary canal at this 

 point bends sharply round upon itself, and the 

 intestine runs nearly parallel with the oesophagus to open into 

 the mantle-cavity as already described. 



A pair of glands (Fig. 661, s.g. ; Fig. 663, sal.), which are 

 commonly termed salivary, though their functional correspondence 

 with salivary glands has not been proved, are situated in the 

 head behind the cranial cartilage. The ducts of these two glands 

 run inwards and unite to form a median duct, which opens into 



Fi<:. (557. Sepia 

 cultrata, nuchal 

 cartilage. 



