MOLLUSCA 219 
ganglia, which give off ten large nerves, one to each arm; they 
also supply the siphon. The auditory nerves also arise from 
the pedal ganglia, although their fibres may be traced to the 
cerebral. The pedal ganglia are partially marked off from the 
fused pleural and visceral by the presence of a small foramen 
through which a blood-vessel passes. From the pleural por- 
tion of this compound nerve centre a stout nerve passes to the 
stellate ganglion, situated at the angle between the mantle and 
the head. It can be seen shining through the integument 
when the mantle cavity is exposed. From this ganglion nerves 
radiate to the muscles of the mantle. The visceral half of the 
fused ganglion gives off a pair of stout visceral nerves, which 
unite to form a loop. These visceral nerves supply the gener- 
ative organs, the kidneys, and other viscera, and each sends a 
stout branch to a ctenidium. 
The eyes of Sepia are of great complexity. They have a 
striking but superficial resemblance to the Vertebrate eye, and 
fundamental differences exist between these two types of visual 
organs. Anteriorly the eye is covered by a transparent cornea, 
which in Sepia is closed. The cornea is protected by certain 
folds of skin, which can cover it in by the contraction of a 
sphincter muscle, and there is also a horizontal lower eyelid. 
Within the cornea is the anterior chamber of the eye, into 
which the folds of the iris project; they partially cover the 
lens, which consists of an outer and an inner part separated by 
a membrane. The lens is supported by the ciliary body, which 
with the lens occupies the anterior half of the retinal chamber. 
The retina, which completes the wall of this chamber, is two- 
layered, and the nerves which pass to it from the optic ganglion 
enter the retina posteriorly. 
The auditory apparatus consists of two otocysts sunk in 
the cephalic cartilage. Their cavities have an irregular shape, 
and are lined by an epithelium, which is ciliated in places, 
they contain an endolymph, in which a single spherical otolith 
floats. 
An olfactory function is attributed to two small invagina- 
tions of the skin, situated one just behind each eye. The sacs 
open to the exterior by a small sht-like aperture; they are 
lined by a ciliated columnar epithelium, amongst which are 
