U6 AFFINITIES CONNEOTING 



size, and they consequently supplant many smaller and 

 feebler groups. Thus, we can account for the fact that 

 all organisms, recent and extinct, are included under a few 

 great orders and under still fewer classes. As showing 

 how few the higher groups are in number, and how widely 

 they are spread throughout the world, the fact is striking 

 that the discovery of Australia has not added an insect 

 belonging to a new class, and that in the vegetable king- 

 dom, as I learn from Dr. Hooker, it has added only two or 

 three families 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 degree inter- 

 mediate between existing groups. As some few of the 

 old and intermediate forms have transmitted to the present 

 day descendants but little modified, these constitute our so- 

 called osculant or aberrant species. The more aberrant 

 any form is, the greater must be the number of connecting 

 forms which have been exterminated and utterly lost. 

 And we have evidence of aberrant groups having suffered 

 severely from extinction, for they are almost always repre- 

 sented 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, in- 

 stead of as at present by a single one, or by two or three. 

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

 aberrant groups as forms which have been conquered by 

 more successful competitors, with a few members still 

 preserved under unusually favorable conditions. 



Mr. Waterhouse has remarked that when a member 

 belonging to one group of animals exhibits an affinity to a 

 quite distinct group, this affinity in most cases is general 

 and not special; thus, according to Mr. "Waterhouse, of all 

 Eodents, the bizcacha is most nearly related t© Marsupials; 

 but in the points in which it approaches this order, its 

 relations are general, that is, not to any one Marsupial 

 species more than to another. As these points of affinity 

 are believed to be real and not merely adaptive, they must 



