CLASSIFICATION. 273 



which are included in a class, though they transgress the defi- 

 nition of it, may probably surprise the reader. They are so 

 contrary to many of the received opinions respecting the use 

 of definitions, and the nature of scientific propositions, that 

 they will probably appear to many persons highly illogical and 

 unphilosophical. But a disposition to such a judgment 

 arises in a great measure from this, that the mathematical 

 and mathematico-physical sciences have, in a great degree, 

 determined men's views of the general nature and form of 

 scientific truth ; while Natural History has not yet had time 

 or opportunity to exert its due influence upon the current 

 habits of philosophizing. The apparent indefiniteness and 

 inconsistency of the classifications and definitions of Natural 

 History belongs, in a far higher degree, to all other except 

 mathematical speculations ; and the modes in which approxi- 

 mations to exact distinctions and general truths have been 

 made in Natural History, may be worthy our attention, even 

 for the light they throw upon the best modes of pursuing truth 

 of all kinds. 



" Though in a Natural group of objects a definition can 

 no longer be of any use as a regulative principle, classes 

 are not therefore left quite loose, without any certain standard 

 or guide. The class is steadily fixed, though not precisely 

 limited ; it is given, though not circumscribed ; it is deter- 

 mined, not by a boundary line without, but by a central 

 point within ; not by what it strictly excludes, but by what 

 it eminently includes ; by an example, not by a precept ; 

 in short, instead of a Definition we have a Type for our 

 director. 



"A Type is an example of any class, for instance a species 

 of a genus, which is considered as eminently possessing the 

 character of the class. All the species which have a greater 

 affinity with this type -species than with any others, form the 

 genus, and are arranged about it, deviating from it in various 

 directions and different degrees. Thus a genus may consist 

 of several species which approach very near the type, and of 

 which the claim to a place with it is obvious ; while there 

 may be other species which straggle further from this central 



VOL. II. 18 



