130 FRESH WATER FISHES. 



ing discoverable in their external configuration, nor 

 in the internal organization of the viscera, which 

 can explain why it is necessary to reside in the 

 one place or the other, or what obliges them 

 to alternate from the salt to the fresh water. 



Physiology, as yet, has thrown no light on this 

 subject, which is only another evidence of the lim- 

 ited knowledge we possess of the wonderful ope- 

 ration of the laws that govern animal hfe. The 

 rationale of the effect of the two kinds of water, 

 must be sought for in the influence exerted by 

 certain salts, in solution, on the atmospheric air 

 with which they are commingled. 



In the commencement of this essay, the fact has 

 been adverted to, that fishes do not breathe either 

 water or air, exclusively, but a mixture of both. 



By the examination of a map of the United 

 States, or Massachsuetts in particular, it will be ob- 

 served that the origin of the water-courses in the 

 country, are such, that by passing over different 

 soils, in which various ores and other mineral pro- 

 ductions are directly exposed to the action of the 

 stream, they become impregnated or altered in 

 quality, according to the distance they run to- 

 wards the sea. 



Particular families are fitted by the All- Wise 

 Creator, to exist in particular regions, and at par- 

 ticular localities ; — and they are endowed with a 



