MOLLUSCS. 421 



encircles the gullet, contributes to the formation of the 

 large ganglia which supply the arms — the optic and audi- 

 tory nerves — those for the funnel, the tunic, and the vis- 

 cera. From the size of the animals, the ganglia of the 

 nerves are very distinctly displayed. The anastomosing 

 branches of the nerves of the arms are likewise conspicu- 

 ous. 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 roimd 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 appears 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 in- 

 ner 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. 

 Immediately within its cavity, there is a bag, with a pecu- 

 liar membranaceous covering, which contains numerous 

 glandular bodies, similar to the milt of fishes, by which the 

 eye is supported, and which probably act as secreting or- 

 gans (although M. Ccvier could not detect any excretory 

 canals), and likewise an expansion or ganglion of the optic 

 nerve. The concave or anterior surface embraces the cho- 

 roides. This membrane, after enclosing the vitreous hu- 

 mour, forms a zone or diaphragm, which may be compar- 

 ed to the ciliary processes, with an aperture in the centre 

 for the reception of the crystalline lens. The circular 

 margin of this aperture is lodged in a circular groove, and 



