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 thie 
inner side, which may be compared to the sc/erotica, differs 
in many particulars from the covering of the same name in 
the eyes of thevertebral 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 
