230 FISHES. 



view of the nature and organization of fishes he 

 proceeds as follows. 



The watery element where fish were appointed to 

 reside, not being, as already noticed, liable, like the 

 atmosphere, to great and rapid alternations of heat 

 and cold ; and the blood offish remaining in a tem- 

 perature often lower than the surrounding fluid, none 

 of the greater divisions of this class of animals are 

 so strictly confined to either high or low latitudes, 

 as those of others breathing the air. But there is a 

 circumstance affecting fish, to which, in their turn, 

 animals with lungs are strangers ; namely, the dif- 

 ference in density and chemical properties between 

 fresh and salt water ; the species belonging to each 

 being unable to exist in the medium proper for the 

 other, excepting some which pass with impunity from 

 one into the other at pleasure, or during certain 

 seasons. In other respects few natural families are 

 without some genus or species to represent the forms 

 and duties of its congeners in every sea. It is true, 

 that we are not acquainted with what species, or in 

 what numbers, the great depths of the ocean are 

 more particularly inhabited ; but as we may infer, by 

 analogy, from the conditions of existence in all the 

 vertebrated animals ; that life undei; a continually 

 increasing pressure, in proportion to the depths of 

 the superincumbent column of water, must, at a 

 given point reach the limit, where eternal darkness 

 renders the organs of sight unavailing, and conse- 

 quently where the power of obtaining or avoiding 

 prey becomes impossible ; still lower, where all the 

 action of animal life must cease ; where the gravity of 

 no animal matter will descend, and, finally even 

 where metals must remain suspended, many at- 

 mospheres of water above these, we may therefore 

 conclude to be the region where fish in a natural 

 state can reside, comparatively, in short, at no great 

 depth, and possibly not far below one hundred fathoms 

 we must look for the lower limit of their active ex- 

 istence, for the bottom of the sea, already, before 



