THE MODERN STUDY OF ZOOLOGY 13 



connected with them as yet, but destined ultimately 

 to be so, other small centres lying at a distance 

 from the large ones, and constituting distinct 

 types, and, finally, isolated houses representing 

 species of animals widely separated from their 

 fellows, and forming for the time at any rate small 

 but distinct types of their own. 



The distinguishing characteristics of classification 

 by type, and especially the points in which it con- 

 trasts most strongly with classification by definition, 

 have been admirably stated by the late Master of 

 Trinity College in the following words : "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 possess- 

 ing the characters of the class. All the species 

 which have a greater affinity with the type-species 

 than with any others form the genus, and are 

 ranged about it, deviating from it in various direc- 

 tions and different degrees."* 



Such a classification represents the real affinities 

 of animals much more truthfully than classification 

 by definition. The sharp boundary lines, of which 

 nature knows nothing, and which formed the main 



* Whewell, " The Philosophy of the Inductive Sciences," 

 vol. i. pp. 476-7. 



