590 CEPHALOPODA. 



inspiration, along the nasal passages, and, being thus examined with a 

 minuteness of appreciation proportionate to the extent of the olfactory 

 membrane, give intimations of the existence of distant bodies scarcely 

 inferior to those obtained from sight and sound. But, in an aquatic 

 medium, information derived from this sense must be restricted within 

 far narrower limits, inasmuch as the dissemination of odoriferous par- 

 ticles must necessarily be extremely slow, and the power of perceiving 

 their presence comparatively of little importance, seeing that the extent 

 to which it can be exercised is so materially circumscribed. Smell, in 

 aquatic animals, is therefore apparently reduced to a mere perception of 

 the casual qualities of the surrounding element, without any power of 

 inhaling odours from a distance. Simple contact between a sufficiently 

 extensive sentient surface and the water in which it is immediately 

 immersed is all that is requisite in the case before us ; and if an organ 

 can be pointed out, constructed in such a manner as to adapt it to fulfil 

 the above intention, there can be little hesitation in assigning to it the 

 office of an olfactory apparatus. 



(1581.) In Nautilus, the part indicated by Professor Owen* as ap- 

 propriated to the sense of smell consists of a series of soft membranous 

 laminae (fig. 289, I \ fig. 291, h) compactly arranged in a longitudinal 

 direction, and situated at the entry of the mouth, between the internal 

 labial processes. These laminaa 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 towards the sides. They are supplied by nerves 

 (fig. 291, 10) from the small ganglia (8) which are connected with the 

 ventral extremities of the anterior suboesophageal ganglia, and from 

 which the nerves of the internal labial tentacula are likewise given off. 



(1582.) The structure of the eyes in the two divisions of the CEPHA- 

 LOPODA differs remarkably, and in both is so entirely dissimilar from 

 the usual organization met with in other classes of animals, that we 

 must invite the special attention of the reader to this portion of their 

 economy. 



(1583.) In the TETBABBANCHIATA, of which the Nautilus is the only 

 example hitherto satisfactorily investigated, according to Professor 

 Owen's observations t the eye appears to be reduced to the simplest 

 condition that an organ of vision can assume without departing alto- 

 gether 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 obsctira, and a nerve of ample size is appropriated to receive 

 the impression, yet the parts which regulate 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 

 OwenJ, the Nautilus approximates the Gasteropods, numerous genera 

 of which, and especially the PECTINIBBANCHIATA of Cuvier, present ex- 



* Mem. on Nautilus, p. 41. t Loc. cit. p. 39 et seq. J Op. tit. p. 51. 



