II OF THE NATURAL HISTORY SCIENCES 51 



Rosaceae, for instance, or the class of Fishes, is not 

 accurately and absolutely definable, inasmuch as 

 its members will present exceptions to every 

 possible definition ; and that the members of the 

 class are united together only by the circumstance 

 that they are all more like some imaginary average 

 rose or average fish, than they resemble anything 

 else. 



But here, as before, I think the distinction has 

 arisen entirely from confusing a transitory imper- 

 fection with an essential character. So long as 

 our information concerning them is imperfect, we 

 class all objects together according to resemblances 

 which we feel, but cannot define ; we group them 

 round types, in short. Thus if you ask an ordinary 

 person what kinds of animals there are, he will 

 probably say, beasts, birds, reptiles, fishes, insects, 

 &c. Ask him to define a beast from a reptile, and 

 he cannot do it : but he says, things like a cow or 

 a horse are beasts, and things like a frog or a 

 lizard are reptiles. You see he does class by type, 

 and not by definition. But how does this classifi- 

 cation differ from that of the scientific Zoologist ? 

 How does the meaning of the scientific class -name 

 of "Mammalia" differ from the unscientific of 

 " Beasts " ? 



eminently possessing the characters of the class. All the species 

 which have a greater affinity with this type-species than with 

 any others, form the genus, and are ranged about it, deviating 

 from it in various directions and different degrees." WHE- 

 WELL, The Philosophy of the Inductive Sciences, vol. i. pp. 476, 



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