SMELL. 



3(J7 



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 



Sc-^N, 389 



against them. According to GeofFroy 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 Dumeril, 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 at- 

 mospheric 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 those of the mammalia, although they do 

 not, as in the latter class, open into the res^^iratory 

 organs, is shown by the curious transformation of 

 the one into the other during the developement of 

 the tadpole, both of the Frog and of the Salaman- 

 der. We have already seen that during the first 

 periods of their existence, these animals are per- 

 fectly aquatic ; breathing water by means of gills, 



