262 



the animal is without doubt, analogous to our breath* 

 ing, but it is not air, but water, that the fish actu- 

 ally takes in and throws out through the gills at every 

 motion. 



The manner of its breathing seems to be this. The 

 fish first takis a quantity of water by the mouth, 

 which is driven to the gills, these close and keep the 

 water so swallowed from returning by the mouth, 

 while the bony covering of the gills prevents it from 

 going through them, until the animal has drawn the 

 proper quantity of air from the body of water 

 thus imprisoned : then the bony covers open and 

 give it a free passage ; by which naeans also the 

 gills again are opened, and admit a fresh quantity of 

 water. Should the fish be prevented from the free 

 play of its gills, or should the bony covers be kept 

 from moving, by a string tied round them, the animal 

 would soon fall into convulsions and die in a few mi- 

 nutes, 



9. The chief instruments in a fish's motion are the 

 fins, which in some are much more numerous than in 

 others. A fish completely fitted for sailing is fur- 

 nished with two pair ; also three single fins, two 

 above and one below. Thus equipped it migrates 

 \tith the utmost rapidity, and takes voyages of a 

 thousand leagues in a season. But such fish as have 

 the greatest number of fins have not always the swift* 

 est motion. The shark is one of the swiftest swim- 

 xners, yet it wants the ventral fins ; the haddock does 

 not move so swift, though it has them. 



The tins not only assist the animal in progression, 

 but in rising or sinking, in turning, or even leaping 

 out of the water. To answer these purposes, the pec- 

 toral fins serve like oars, to push the animal forward. 

 They are placed behind the opening of the gills ; 

 they are generally large and strong, and answer the 

 same purposes to the fish as wings do to a bird. 

 Those also balance the fish's head, when it is too 



