350 SENSE OF SMELL IN FISHES. 



frequently communicating with the mou<h, in all the j^lk^ 

 giostomes, as the ray, the shark, &c. 



In all fishes these cavities present a kind of sinus, or 

 cul-de-sac with a narrovr opening; most commonly divided 

 into two portions, sometimes into three, as in the eel, by 

 a membranous septum, variously convoluted, which icthyo- 

 logists have frequently noticed as characteristic of species. 



We know from the observations of Monro, that these 

 valves or curtains may be moved according to the will of 

 the animal; and that under certain circumstances the orifice 

 may be nearly covered by the septum. It is easy to ob- 

 serve this in live fishes, as I have seen in the goldfish and 

 stickleback. It is then apparent, that the motion of the 

 septum seems to be the consequence of the protraction of 

 the lips; since at each inspiration *the catity opens and di- 

 lates, while it contracts and is covered as often as th6 

 mouth is closed: whence it seems to follow, that at every 

 inspiration the fish causes a small quantity of water to enter 

 on each side, which it may be said thus to analyse. 

 The first pair Each of these perforations exhibits within a cavity, very 

 of nerves and spacious in proportion to its orifice; and on this is spread 

 part of the 5ih f .. / u , .x». • i. r. \ 



spread on the the sentient membrane covered with mucus, in the substance 



menibrane of which is expended the whole of the first pair of cerebral 

 nerves, and one or more large branches of the fifth pair, 

 according to the observation of Collins quoted and cor- 

 rected by Cuvier. 



iThese cavities Nor must I forget to remark, as a circumstance particu- 



are always se- j^rly deserving notice, that these pretended nasal cavities 

 parated from -^ ^ * ° ,' , ,^ .. , 



the respiratory are always separated from the canal of respiration* and 



^i^^^» that it is only in the rays, and some neighbourirtg genera, 



which have spiracles, that they are observed almost in the 



mouth. In fact it is to be presumed, that the liquid, in 



traversing them, would have deadened the sensibility of 



their surface by the rapidity of its motion, and the friction 



of its particles. 



Wh^tarethe Now are these peculiarities of structure, which I have 



inferences from mentioned, of such a kind as to lead us to abandon our 



first opinion, deduced from the knowledge of physics, that 



smells cannot be perceived in water? or is not this supposed 



organ of smell in fishes better adapted to excite in them the 



sensation 



