46 Sketch of the Life of the late Professor Edward Forbes. 



phaenotnenon of a point of maximvm number of species is seen, witli 

 fewer and fewer species radiating, as it were, from it. [This is what 

 I speak of under C, as more centres than one in geographical space.] 



Area of a genus. 



-5. 



The numbers refer to species. 



[This diagram is imaginary.] 



Thus, Viola has an American as well as an Old World point of maxi- 

 mum of development, around which you may group the species, 

 gradually diminishing in number. 



" In time, however (or, in other words, in geological distribution), 

 so far as we know, each generic type has had, so to speak, an unique 

 and continuous range : — 



Palaeozoic 



Thus we find that all the species of genus a are grouped together 

 within a succession of formations which commence at a certain point, 

 and cease at another ; so with b, so with c ; but when once a generic 

 type (as Trilobites) has ceased, it never reappears. Therefore I speak 

 of a genus having an unique centre in time. 



" tinder italic c I say, that a genus is an abstraction, a divine 

 idea. I think the very fact of the centralization of groups, of allied 

 species, i. e. of genera, in space and time, is sufficient proof of this. 

 Doubtless we make many so-called genera that are artificial ; 

 but a true genus is natural ; and, as such, is not dependent on 

 man's will. 



" 1 dare say that I have only added obscurity to obscurity by this 

 explanation ; but, with diagrams, and time for talk, I think I could 

 make the matter quite clear. 



" Yours very sincerely, 



"Edward Forbes." 



He was elected in 1853 to the Presidentship of the Geological 

 Society; and delivered, on leaving that office, an admirable 



