39 



small ganglion (16. pi. 7.), which distributes nerves to the viscera. Other minute 

 nerves (17. pi. 7.) arise mesiad of the origins of the preceding pair, and form a 

 network upon the muscular parietes of the vena cava, accompanying that vessel 

 as far as the pericardium, and being lost on the ventricle and glandular parts 

 contained therein. 



As there has been occasion to observe a degree of inferiority in the brain of 

 Nautilus, so also we find a corresponding simplicity in the eye, which is far 

 from presenting those complexities of structure that render it so remarkable 

 an organ in the Dibranchiate Cephalopods. Indeed it here appears to be re- 

 duced to the simplest condition that the organ of vision can assume, without 

 departing altogether from the type which prevails throughout the higher classes. 

 For although the light is admitted by a single orifice into a globular cavity or 

 camera ohscura, and a nerve of ample size is appropriated to receive the im- 

 pression, yet the parts which regulate the admission and modify the direction 

 of the impinging rays are entirely deficient. 



It has been previously remarked, that the eyes are not contained in orbits, 

 but are attached each by a pedicle to the side of the head, immediately below 

 the posterior lobes of the hood. The ball of the eye {s. pi. 1 ; f . pi. 2 ; o. pi. 7.), 

 is about eight lines in diameter, and although contracted and wrinkled in the spe- 

 cimen, appears to be naturally of a globular form, rather flattened anteriorly. The 

 diameter of the pedicle {t. pi. 1 ; p. pi. 7.) is three lines, and its length the same. 

 On each side of the pedicle is the orifice of a sheath excavated in the substance 

 of the hood, and containing the peculiar tentacles previously described {r.r. pi. 1 .). 

 Along the inferior border of the eye there is a slightly elevated ridge {u. pi. 1 . & 2.), 

 as it were a rudiment of an inferior eyelid, and from the middle of this ridge a 

 smaller one {v. pi. 1.) is continued to the middle of the anterior surface of the 

 eye, where the pupil (w. pi. 1 ; q. pi. 7.), which is a circular aperture less than a 

 line in diameter, is situated. The small size of the pupil in this species is the 

 more remarkable when contrasted with the magnitude of that aperture in the Di- 

 branchiate Cephalopods ; but it depends most probably on the great degree of 

 mobiUty which the eye of the Pearly Nautilus enjoys, in consequence of its at- 

 tachment to a muscular pedicle, which enables it to be brought to bear with 

 ease in a variety of directions ; w'hilst in the preceding genera corresponding 

 motions of the head and body would have been necessary, on account of the 



