SMELL. 



291 



into two cavities, and serving the purpose of preventing the 

 introduction of any foreign body. The organ itself is si- 

 tuated behind this valve, and consists either of a membrane, 

 curiously plaited into numerous semicircular folds, or of 

 tufted or .arborescent filaments. Fig. 3SS shows this cavity 



(s,) with its plaited membrane in the Perch; and Fig. 3S9, in 

 the Skate; the laminae in the former being radiated, and in 

 the latter, foliated, or parallel to each other. On the sur- 

 face of these organs, whatever be their. shape, the olfactory 

 nerves (n,) arising from the anterior lobes (o) of the brain, 

 are distributed; and the great size of these nerves would 

 lead us to infer considerable acuteness in the sense which 

 they supply. When the fish is swimming, their situation in 

 front of the snout exposes them to the forcible impulse of 

 the water which strikes against them. According to Gcof- 

 froy St. Hilaire, the water enters the cavity by the upper 

 orifice, and escapes by the lower. Scarpa alleges that fishes 

 exercise this sense by compressing the water against the 

 membrane. On the other hand, it is contended by Dumerll, 

 that the perceptions communicated by this organ, being the 

 result of the action of a liquid instead of a gas, should be 

 classed under the head of taste rather than of smell. This 

 seems, however, to be a mere verbal criticism, in making 

 which it appears to have been forgotten that the impressions 

 of odorous effluvia, even in animals breathing atmospheric 

 air, always act upon the nerve through the intermedium of 

 the fluid which lubricates the membrane of the nostril. 

 That the nasal cavities of fishes are rudimental forms of 



