464 CEPHALOPODA. 



appropriated to the sense of smell, consists of a series of soft 

 membranous laminae (Jig. 210, I ; fig. 212, g) compactly arranged 

 in the longitudinal direction, and situated at the entry of the 

 mouth, between the internal labial processes. These laminae are 

 twenty in number, and are from one to two lines in breadth, and 

 from four to five in length, but they diminish in this respect to- 

 wards the sides. They are supplied by nerves (Jig. 212, 10) from 

 the small ganglions (8) which are connected to the ventral extremi- 

 ties of the anterior sub-cesophageal ganglia, and from whence the 

 nerves of the internal labial tentacula are likewise given off. 



(506.) The structure of the eyes in the two divisions of the 

 Cephalopoda differs remarkably, and in both is so entirely dissimi- 

 lar from the usual organization met with in other classes of animals, 

 that we must invite the special attention of the reader to this por- 

 tion of their economy. 



In the TETRABRANCHIATA, of which the Nautilus is the only 

 example hitherto satisfactorily investigated, according to Professor 

 Owen's observations* the eye appears to be reduced to the simplest 

 condition that an 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 obscura, and a nerve of ample size 

 is appropriated to receive the impression, yet the parts which re- 

 gulate the admission, and modify the direction of the impinging 

 rays, were, in the specimen examined, entirely deficient. In this 

 structure of the eye, observes Professor Owen,*f- the Nautilus ap- 

 proximates the Gasteropods, numerous genera of which, and espe- 

 cially the PECTINIBRANCHIATA of Cuvier, present examples analo- 

 gous in simplicity of structure, and in a pedicellate mode of support 

 and attachment to the head. Moreover, as the Pearly Nautilus, 

 like the latter group of mollusks, is also attached to a heavy shell, 

 and participates with them in the deprivation of the ordinary lo- 

 comotive instruments of the Cephalopods, the anatomist whose 

 remarks we quote hence deduces the more immediate principle of 

 their reciprocal inferiority with respect to their visual organ, observ- 

 ing that it would little avail an animal to discern distant objects, 

 when it could neither overtake them if necessary for food, nor avoid 

 them if inimical to its existence. 



The eyes of Nautilus (Jig. 205, m) are not contained in orbits, 

 but are attached each by a pedicle to the side of the head, im- 



* Mem. on Nautilus, p. 39, et seq. f Op. cit. p. 51. 



