20 SATUllDAY LECTURES. 



Such are, in brief, a few of the distinctions between fishes 

 and mammals. 



The class of mammals contains forms fitted for progres- 

 sion on land, as bipeds (man) and quadrupeds; for flight in 

 the air, i\s bats; and for exclusive life in the water, as 

 whales. 



The class of fishes comprises not only animals with the 

 usual fish-like form exemplified in the salmon and perch, 

 but broad flattened fishes like the angler or goose-fish, and 

 others of snake-like form as the eels. 



Mere form, then, is of no consequence in the determina- 

 tion of the major relations of animals and is of importance 

 only in ascertaining the relations of minor groups. Every 

 t3^pe of nature which we examine brings to us evidence of the 

 truth of this proposition. Animals which have the great- 

 est external resemblance may be, when anatomically con- 

 sidered, most unlike, and vice-versa, animals which are 

 very different in external appearance, may exhibit great 

 similarity in internal structure. I might adduce very num- 

 erous illustrations of the prevalence of this truth, but the 

 advancing moments warn me that I must bring my re- 

 marks to a termination. I shall, therefore, conclude with 

 certain deductions that are to be derived from the studies 

 in which ^ye have been engaged, and justify the title which 

 1 have selected for the discourse, by a contrast of the 

 methods involved in the classification of the animals we 

 have been examining. 



The uninstructed observer instinctively considers animals 

 with regard to their external form. 



The naturalist has learned to distrust external form, and 

 to consider internal structure as paramount. 



The ordinary observer regards as of great moment the 

 relation of an animal to its surroundings and mode of 

 progress — whether in land, in water, or through air. 



The zoologist has learned that the adaptations for different 

 modes of life may coexist with slight differences in the in- 

 ternal economy. 



