SEPIA, 277 
On each side of the head is a large simple eye; although 
of the simple type the eye is complex in structure. It has 
all the more important parts of the vertebrate 
eye, such as cornea, lens, iris, vitreous humour 
and retina, and is supplied by large optic nerves from the 
brain. Just behind each eye is a 
ciliated olfactory pit, and near the Fig. 195.—Venrrat Virw 
brain is a pair of large ofocysts, OF A CUTTLE (Sepia 
Asis to be expected from its free  &cenatis) x }. 
active life, large size and com- / 
plexity of structure, the ‘“cuttle” 
has sense-organs far in advance of 
those found in any other Mollusca. 
The mantle fuses on the lower 
surface to enclose a large mantle- 
cavity which is blind behind but 
opens widely at the neck. Just in 
front of this open- 
ing lies the szphon, 
a tube which opens by a large 
funnel behind into the mantle- 
cavity, and by a small aperture 
forwards under the head. The 
hind edges of the siphon are so 
arranged that water expelled from Note the ten arms with suckers, 
the mantle-cavity passes through t! the mouth between them Tn 
the siphon, but water inhaled “Po” immediately behind it 
passes in between the edges of the siphon and the mantle. 
By muscular contraction the animal forcibly ejects 
water from the mantle-cavity through the siphon, and in 
this manner drives itself backwards through the water. 
If the mantle be cut open along the mid-ventral line and 
thrown back, the interior of the mantle-cavity is exposed. 
The two most conspicuous organs are a pair of large feathery 
ctenidia, consisting of a median axis and lateral branches. 
They are purely respiratory. In the middle line of the 
body the rectum may be seen running forwards and ter- 
minating in the amws. A little further backwards open the 
paired excretory pores and the unpaired genital pore on the 
left side. As in the mussel and the snail, the mantle-cavity - 
is evidently a part of the external surface of the body. 
Sensory. 
Respiratory. 
