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 fit 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 Sepia 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 Sepia 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 
