ALIMENTARY SYSTEM. 379 



Sense Organs. — The eyes are large and efficient. They present a 

 striking resemblance to those of Vertebrates, and, as they are not " brain 

 eyes," they illustrate how superficially similar structures may be developed 

 in different ways and in divergent groups. In cuttlefishes, the eyes lie 

 on the sides of the head, protected in part by the cartilage surrounding 

 the brain, and in part by cartilages on their own walls. 



The eye is a sensitive cup arising in great part from the skin. Its 

 internal lining is a complex retina, on the /wfc;Vor surface of which the 

 nerves from the optic ganglion are dis'iributed. In the cavity of the cup 

 there is a clear vitreous humour. 



The mouth of the cup is closed by a lens, supported by a "ciliary 

 body." The lens seems to be formed in two parts — an outer and an 

 inner plano-convex lens. The pupil or hole in front of the lens is 

 fringed by a contractile iris. 



The outer wall of the optic cup is ensheathed by a strong supporting 

 layer — the sclerotic, which is in part strengthened by cartilage, covered 

 by a silvery membrane, and continued into the iris. 



In front of the eye there is a transparent cornea, and the skin also 

 forms protecting lids. 



Round about the optic ganglion there is a strange "white body," 

 which seems to be a fatty cushion on which the eye rests. 



The two ear sacs, containing a spherical otolith and a fluid, sometimes 

 with calcareous particles, are enclosed in part of the head cartilage, close 

 by the pedal ganglia. The nerves seem to come from the pedals, but it 

 is said that their fibres can be traced up to the cerebrals. 



A ciliated "olfactory sac" lies behind each eye, and is innervated 

 from a special ganglion near the optic. There are no osphradia of the 

 usual type. 



Finally, there are tactile or otherwise sensitive cells on various parts 

 of the body, especially about the arms. 



Alimentary System. 

 The cuttlefish eats food which requires tearing and chew- 

 ing, and this is effected by the chitinous jaws worked by 

 strong muscles, and by the toothed radula moving on a 

 muscular cushion. The mouth lies in the midst of the arms, 

 bordered by a circular lip. Through the ganglionic mass 

 passes the narrow gullet, which leads into the globular 

 stomach, lying near the dorsal end of the body. The 

 stomach is followed by a ca;cum or pyloric sac, and the 

 intestine curves headwards again to end far forward in the 

 mantle cavity. There do not seem to be any glands on the 

 walls of the food canal, the stomach has a hard cuticle, the 

 digestion which takes place there must therefore be due to 

 the digestive juices of the glandular appendages. Of these 

 the most important is usually called the liver; it is bilobed, 

 and hes in front of the stomach attached to the oesophagus. 



