FISHES. 329 



ntious ball, which resembles the cineritious matter connected, 

 in our body, with the olfactory nerve within the cranium. 



When the olfactory nerve arrives behind the folded mem- 

 brane which we have described, it is dilated to be applied 

 to the whole of its internal and convex surface. In some 

 fishes, no previous enlargement takes place, while in others 

 the nerve swells into a real ganglion. When expanded, it 

 has been compared to the retina, but the filaments of which 

 it is composed are more distinct. 



The sense of smell in fishes is supposed by many to fur- 

 nish them with the most delicate tests, for searching after, 

 and distinguishing their food ?. 



We may observe, however, that the well known vora- 

 ciousness of fishes, the eagerness with which they will seize 

 a metal button, or any glittering object, the whole art of 

 artificial bait and fly fishing, all seem to point out the or- 

 gan of sight as the principal instrument by which they dis- 

 cover their food. Besides, the organs of smelling are by 

 no means favourably situated for receiving quickly the im- 

 pressions new objects are calculated to produce. In the 

 chondropterygii the nares communicate by a groove with 

 the angles of the mouth, but in general the organs of smell 



* Dr MUNJIO primus states, that *' if you throw a fresh worm into the 

 water, a fish shall distinguish it at a considerable distance ; and that this is 

 not done by the eye is plain from observing, that, after the same worm has 

 been a considerable time in the water, and lost its smell, no fishes will come 

 near it ; but if you take out the bait, and make several little incisions into it, 

 so as to let out more of the odoriferous effluvia, it shall have the same effect 

 as formerly. Now, it is certain, that had the creatures discovered this bait 

 with their eyes, they would have come equally to it in both cases. In con- 

 sequence of their smell being the principal means they have of discovering 

 their food, we may frequently observe th,em allowing themselves to be car- 

 ried down with the stream, that they may ascend again leisurely against the- 

 current of the water ; thus the odoriferous particles swimming in that me- 

 dium, being applied more forcibly to their organs of smell, produce a strong- 

 er sensation-" Comp. Anat. p. 127, Edin. 1783. 



