INTRODUCTION. 77 



and during floods, or in muddy waters, where we 

 know that vision is much impaired, scent only can 

 bring fish to the bait, which, if employed for a 

 continuance in one spot, will at length attract 

 numbers. But Cuvier hints at this sense being even 

 of service for a purpose of more delicacy that of 

 distinguishing the difference between waters of 

 different streams or currents ; and it is probable, 

 that, by the use of these organs, many of our migra- 

 tory fresh water species are enabled again to dis- 

 cover and return to the rivers they had previously 

 frequented. Such seems the most common dis- 

 tribution of the three most prevalent senses. 

 Various, however, are the modifications of their 

 application, corresponding with the manners and 

 necessities of the individuals. 



The greater proportion of fishes are carni- 

 vorous, and find an abundant and varied food in 

 the immense profusion of moluscous animals, as 

 well as in the smaller species of their own orders, 

 for among them may be said to exist a constant 

 system of attack and defence a general war, the 

 stronger against the weaker. A few only subsist 

 on vegetables, " and graze the sea weed, their 

 pasture." The teeth, the only organs almost of 

 prehension, are therefore varied in innumerable 

 forms, but are chiefly adapted either for tearing 

 or bruising. In the cartilaginous fish, we find 

 these forms strongly developed ; those of the 



