Chap. XIII. CLASSIFICATION. 429 



orders, under still fewer classes, arid all in one great 

 natural system. As showing how few the higher groups 

 are in number, and how widely spread they are through- 

 out the world, the fact is striking, that the discovery of 

 Australia has not added a single insect belonging to a 

 new order ; and that in the vegetable kingdom, as I 

 learn from Dr. Hooker, it has added only two or three 

 orders of small size. 



In the chapter on geological succession I attempted 

 to show, on the principle of each group having generally 

 diverged much in character during the long-continued 

 process of modification, how it is that the more ancient 

 forms of life often present characters in some slight 

 degree intermediate between existing groups. A few 

 old and intermediate parent-forms having occasionally 

 transmitted to the present day descendants but little 

 modified, will give to us our so-called osculant or aber- 

 rant groups. The more aberrant any form is, the 

 greater must be the number of connecting forms which 

 on my theory have been exterminated and utterly lost. 

 And we have some evidence of aberrant forms having 

 suffered severely from extinction, for they are gene- 

 rally represented by extremely few species; and such 

 species as do occur are generally very distinct from 

 each other, which again implies extinction. The genera 

 Ornithorhynchus and Lepidosiren, for example, would 

 not have been less aberrant had each been represented 

 by a dozen species instead of by a single one ; but such 

 richness in species, as I find after some investigation, 

 does not commonly fall to the lot of aberrant genera. 

 We can, I think, account for this fact only by looking 

 at aberrant forms as failing groups conquered by more 

 successful competitors, with a few members preserved by 

 some unusual coincidence of favourable circumstances. 



Mr. Waterhouse has remarked that, when a member 



