352 LECTURE XXIV. 



Greek fisliermen were in the habit of attaching strong-scented herbs 

 to their baits to deter the cuttle-fishes from coming to devour 

 them. 



The organ of hearing consists of two vestibular cavities, excavated 

 in the thick and dense part of the cartilaginous cranium which sup- 

 ports the suboesophageal ganglions. In the cuttle-fish several obtuse 

 elastic processes project from the inner surface of the cavity, which 

 contains a delicate sacculus and otolithe. The acoustic nerve is 

 spread over the sacculus, and is impressed by the movements of 

 the otolithes, which respond to sonorous vibrations, which may be 

 strong enough to affect the body generally. In the Octopus the 

 vestibules are nearly spherical with a smooth internal surface ; the 

 otolithe is hemispherical ; in the Eledone it is shaped like the shell 

 of a limpet, with the apex rounded and curved backward. In all the 

 Cephalopods the otolithes consist of carbonate of lime. 



The orbit in the cuttle-fish is formed posteriorly by a thick 

 cartilaginous cup, and is completed anteriorly by a dense white 

 fibrous dermal membrane, which becomes transparent at the anterior 

 part of the globe, and forms the cornea. The cornea and the fibrous 

 tunic are lined by a thin serous membrane, which is reflected over 

 the anterior part of the sclerotica, and through its anterior aperture 

 (to which the cornea does not adhere), like the membrane of the 

 aqueous humour, and is finally continued into the groove of the 

 crystalline lens. 



The space between the eyeball and its capsule, thus circumscribed, 

 is filled with an aqueous humour, by w^hich the cornea is separated 

 from the eyeball, and kept tense. The outer tunic of the proper 

 eyeball is a fibrous membrane covered by the aponeurotic expansion 

 of the muscles of the eye, and with an anterior aperture which is 

 closed by the crystalline lens. Within the fibrous tunic there is a 

 thin cartilaginous coat perforated posteriorly by the numerous 

 fibrils from the optic ganglion. The layer of fibrous membrane is 

 continued from the anterior margin along with the outer fibrous 

 layer to form the pupillary aperture, Avhich is encroached upon by a 

 bilobed process analogous to the curtain, which depends from the iris 

 of the ray. The cartilaginous sclerotic is lined by a thick expansion 

 of the nervous fibres given ofi" from the optic ganglion. These fibres 

 are sent off" from the outer surface of the ganglion, which presents a 

 pulpy texture in its centre. They are grouped into flattened bundles, 

 which decussate each other, as observed by Dr. Power, before 

 perforating the cartilaginous sclerotica, and, after expanding into the 

 retina, extend towards the groove of the crystalline lens, and, being 

 joined by a thin membrane from the anterior margin of the car- 



