1IO FISHES. 



cut through the resisting medium which they in- 

 habit. Some of them are endowed with such ex- 

 traordinary powers of progressive motion, that they 

 are able not only to overtake the fastest sailing ves- 

 sels, but, during their swiftest course, to play round 



i 

 them without any apparently extraordinary ef- 

 forts. 



Their bodies are in general covered with a kind of 

 horny scales, to keep them from being injured by 

 the. pressure of the water. Several are enveloped 

 w r ith a fat and oily substance, to preserve them 

 from putrefaction, and to guard them from extreme 

 cold. 



They breathe by means of those comb-like organs 

 placed on each side of the neck, called gills. In 

 doing this they fill their mouth with water, then 

 drive it backwards with so much force as to lift open 

 the great flap, and force it out behind. And in the 

 passage of this, among the feather-like processes of 

 the gills, all, or at least the greatest part, of the air 

 contained in it, is left behind, and carried into the 

 body to perform its part in the animal economy*. 

 In proof of this fact, it has been ascertained that, 

 if the air is by any means extracted from the wa- 

 ter into which fish are put, they immediately come 

 to the surface and gasp for air. — Distilled water is 

 to fish what the vacuum formed by an air-pump is 

 to most other animals. — This is the reason why in 

 winter, when a fish-pond is entirely frozen over, it 

 is necessary to break holes in the ice, not that the 

 fish may come to feed, but that they may come to 

 breathe. Without this precaution, if the pond is 



