78 INTRODUCTION. 



pressure so enormous. Those who descend in 

 diving-bells, also, to great depths — ^since, of course, 

 the pressure made upon their bodies, in these cir- 

 cumstances, by the air which surrounds them, is 

 always equal to that made upon this air by the 

 water which is in contact with it — are often found 

 to spit blood, and to manifest many other marks of 

 disturbance of their functions, upon rising again to 

 the surface of the water. 



It seems, then, fair to conclude, that it is only 

 to a certain depth below the surface of the water 

 that fishes can descend with impunity ; and that, 

 universally diffused as they may be in pools and 

 most rivers, it is only within a certain determinate 

 range of the ocean that they are capable of existing. 

 This circumstance is not sufficiently often reflected 

 upon, when we unhesitatingly represent fishes as 

 living upon the water-plants which grow at the 

 bottom of the deep, and describe every thing that 

 is thrown into the water as becoming indiscrimi- 

 nately their prey. In all likelihood, the supposed 

 water-plants, growing in many parts of the ocean, 

 never come within the reach of fishes, at any rate, 

 till they have become separated from their parent 

 stalks; and the substances thrown overboard, in 

 many cases, soon pass beyond it, unless they are 

 adroit enough to seize it by the way. There may 

 be, undoubtedly, 



" a thousand fearful wTecks — 



A thousand men that fishes gnaw upon, 

 All scattered in the bottom of the sea," 



