122 MOLLUSCA. 



size of the animals, the ganglia of the nerves are very dis- 

 tinctly displayed. The anastomosing branches of the nerves 

 of the arms are likewise conspicuous. Each nerve, at the 

 base of each arm, sends out two filaments, one to the nerve 

 of the arm on each side. In this manner a chain of nerves 

 is formed round the base of the arm, probably calculated to 

 enable them to act more readily in concert. From the 

 abundant distribution of nerves to the different parts, it ap- 

 pears probable that the sense of touch exists in a tolerably 

 perfect manner. There is no proof of the development of 

 organs for the display of the senses of smell and taste. 



The Cephalopoda are furnished with two eyes, one on 

 each side of the head. The external membrane on the 

 inner side, which may be compared to the sclerotica, differs 

 in many particulars from the covering of the same name in 

 the eyes of the vertebral animals. While it surrounds the 

 contents of the eye from the entrance of the optic nerve to 

 the pupil, it is greatly separated from the choroides. Im- 

 mediately within its cavity, there is a bag, with a peculiar 

 membranaceous covering, which contains numerous glan- 

 dular bodies, similar to the milt of fishes, by which the eye 

 is supported, and which probably act as secreting organs 

 (although M. Cuvier could not detect any excretory canals), 

 and likewise an expansion or ganglion of the optic nerve. 

 The concave or anterior surface embraces the choroides. 

 This membrane, after enclosing the vitreous humour, forms 

 a zone or diaphragm, which may be compared to the ciliary 

 processes, with an aperture in the centre for the reception 

 of the crystalline lens. The circular margin of this aperture 

 is lodgedina circular groove of the lens, andintimately united 

 with it, so that the lens is divided into two unequal hemis- 

 pheres. Its central surface is coated, as in the higher 



