214 ZOOLOGY 



like structure open at both ends. The posterior aperture 

 communicates with the mantle cavity. "When the edges of 

 the mantle are in close apposition to the body-wall, to aid 

 which a pair of cartilaginous nodules exist on the mantle 

 edge, which iit into corresponding depressions on the outside 

 of the funnel, and the muscles of the mantle contract, the 

 water in the mantle cavity is forced violently through the 

 siphon. The result of this is, the Sepia darts backwards. In 

 the lumen of the siphon is a small valve which only allows 

 the water to pass one way ; this possibly represents the hind- 

 foot or metapodium. 



The cuttle-bone or shell of Stipia is entirely internal. It 

 lies along the dorsal surface in a sac formed by the concres- 

 cence of certain folds of the mantle in this region (Fig. 126). 

 It consists of a posterior horny portion, which is continued 

 forward by a series of calcareous plates deposited by the 

 inner wall of the sac ; between these plates air is found. This 

 air must be secreted by the surrounding tissues, it probably 

 assists the Seipia to balance itself. 



If the mantle be divided and the mantle chamber exposed, 

 the anus will be seen situated in the middle line near the 

 posterior end of the siphon. Close to it the duct of the ink 

 sac opens. A little way behind the anus, and on each side of 

 it, is situated a nephridial opening, and at about the same 

 level on the left side is the aperture of the genital duct. 

 The large ctenidia lie one on either side, and in the female 

 Sepia a pair of large nidamental glands are to be seen through 

 the body-wall. 



The mouth is surrounded by a circular lip and guarded by 

 two strong horny beaks resembling those of a parrot, except 

 for the fact that the under beak is the larger and more pro- 

 minent (Fig. 126). The buccal mass is large and muscular, it 

 contains a well-developed radula. The rows of teeth consist 

 of five central conical teeth and one hook - shaped tooth on 

 each side. The oesophagus, a narrow tube, passes from the 

 buccal mass straight to the posterior end of the body, and 

 opens into a thick-walled stomach. At this point the intes- 

 tine bends forward ventrally, and gives off a curved caecum of 

 considerable size. From this the rectum passes along the 



