80 INTRODUCTION. 



THE LOCOMOTION OF FISHES. 



In the preceding chapter we detailed the principal 

 means by which fishes, on the one hand, preserve 

 their level in the water which they inhabit, and, on 

 the other rise, and, within certain limits sink in 

 this fluid, according to circumstances. These pro- 

 cesses are, or may be all, in a great measure 

 passive ; but those by which these animals effect 

 their various locomotions, otherwise than perpendi- 

 cularly upwards or downwards, by which they 

 creep along, or into the mud or sand at the bottom 

 of the water, or, even deserting their natural ha- 

 bitat, crawl along the grass, or climb trees, as well 

 as those by which they perform their various evo- 

 lutions in the water, leap occasionally from its 

 surface, and even skim for some space through the 

 air, are strictly active, and fall now to be considered. 

 It is not, indeed, improbable, that some fishes, 

 like the duck-weed and star-grass among plants, 

 and the sea-blubber, and many other invertebrate 

 tribes, among animals, may be moved in the water 

 principally ]>y the currents and tides, or by the 

 winds ; but the number of those in which loco- 

 motion is otherwise than active, is certainly very 

 small. 



The chief organs of locomotion in fishes are the 



