4S 



INTRODCCTIOX. 



PISHES, IN RELATION TO OTHER ANIMALS. 



By people altogether uneducated, every animal 

 is regarded as a fish which is an inhabitant of 

 the water; and although persons somewhat bet- 

 ter informed do not use the term in quite so 

 comprehensive a sense as this, but exclude the 

 animals commonly called shell-fish, belonging to 

 those classes which are destitute of an internal 

 skeleton, they still commonly embrace under this 

 title all the inhabitants of the waters which possess 

 such a skeleton, and which move by fins. Even 

 this, however, is a more extensive sense than that 

 in which the word Fish is employed by Naturalists, 

 who confine this appellation to an animal which, 

 besides being possessed of the above-mentioned 

 characters, breathes by means of gills, and not by 

 true lungs, has a single instead of a double heart cir- 

 culating cold instead of warm blood. Now, this is not 

 the case with whales, dolphins, porpoises, and many 

 other tribes of aquatic animals ; all of which breathe 

 by lungs, have a double heart, aie waim-blooded, 

 and are, consequently, with propriety, excluded from 

 the class of fishes. The whale, and other aquatic 

 animals, resemble the mammalia in their structure 

 and it is, accordingly, in the same class that they 



