170 



" slowly developed," my meaning may possibly require 

 some slight comment. It is simply therefore to guard 

 against the fallacy, which I have so often disclaimed, 

 that genera are abruptly (or suddenly) terminated on 

 their outer limits, that the expression has been employed. 

 Though I believe that a series of species, each partially 

 imitating the next in contact with it, is Nature's truest 

 system ; yet we must be all of us aware that those 

 species do certainly tend, in the main, to map out 

 assemblages of divers phases and magnitudes, distin- 

 guished by peculiar characteristics which the several 

 members of each squadron have more or less in common. 

 So that it is only in the middle points that these various 

 groups, respectively, attain their maximum, every one 

 of which (by way of illustration) may be described as a 

 concentric bulb, which becomes denser, as it were, in its 

 successive component layers, and more typical, as it 

 approaches its core. 



If, then, the theory of genera be such as I have endea- 

 voured to expound, it results from what has been said, 

 that every generic type is to be looked for in, or about, 

 tJie centre of its peculiar group, or at any rate in that 

 region of it which would seem to be the most charac- 

 teristically, or evenly, pronounced. I lay particular 

 stress upon this conclusion, because (if correct) it will 

 somewhat modify the notions which are occasionally 

 entertained upon the subject. A stricture, however, 

 may here be required upon what I have advanced, lest, 



