330 PHILOSOPHY OF ZOOLOGY. 



have no communication wjth those of mastication oi' respi- 

 ration ; and, as the external openings are narrow, and but 

 ill supplied with muscles, we are at a loss to conceive in 

 what manner the water impregnated with odoriferous parti- 

 cles can be thus rapidly applied to the extremities of the 

 olfactory nerve. The same water must pass through the 

 mouth, and be spread over the extended surface of the gills ; 

 so that we may presume, until farther light be thrown on 

 the subject, that these latter organs may likewise contribute 

 to warn the fish of the presence or absence of salutary or 

 noxious impregnations. 



The organs of smell furnish the ichthyologist with some 

 important characters in the description of the species. These 

 have hitherto been too much neglected, although they have 

 the advantage of being permanent. 



The Eyes of fishes, like all other red-blooded animals, 

 are two in number. They vary greatly in position, both 

 being, in some species, on the same side of the head, as in 

 flounders ; while in others they are nearly vertical. In ge- 

 neral, however, they are placed one on each side of the 

 head. The eyes of fishes are larger in proportion to the 

 size of their bodies, than in quadrupeds, as we find the eye 

 of the cod-fish equal in size to that of an ox. 



Fishes, in general, are destitute of eye-lids, and are sel- 

 dom even furnished with projections in place of eye-browst. 

 In the moon-fish (Tetraodon mola), however, the eye may 

 be entirely covered with an eye-lid, perforated circularly. 

 In the greater number of fishes, the skin passes directly 

 over the eye, without forming any fold ; and in some cases, 

 it does not adhere very closely to the eye. Thus the com- 

 mon eel and lampry may be skinned without producing any 

 hole in the situation of the eye, the skin only exhibiting at 

 that place a round transparent spot. In the trunk-fish 

 (Ostracion), the conjunctiva, or external covering of the 



