Chai-. XIII. ORGANIC BEINGS. 337 



under a few p^rcat orders, and under still fewer classes. As 

 sho\vin<j:; how few the hi<>her frroups are in number, and how 

 widely they are spread throuf^hout the world, the fact is strik- 

 in;i-, that the discovery of Australia has not added an insect 

 l)(>l()n<2,"iiij^ to a new class ; and that in the vegetable kingdom, 

 as I learn fi-om 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 

 nuich in character during the long-C(jntinued process of modifi- 

 cation, how it is that the more ancient forms of life often pre- 

 sent characters in some degree intermediate between existing 

 groups. Some few of these old and intermediate forms hav- 

 ing transmitted to the present day descendants but little modi- 

 lied, constitute our so-called osculant or aberrant species. The 

 more aberrant any form is, the greater must be the number 

 of connecting forms Avhicli have been exterminated and utterly 

 lost. And we hav(! some evidence of aberrant groups having 

 suffered severely from extinction, for they are almost always 

 represented by extremely f(jw species ; and such species as do 

 occur are generally very distinct from each other, which again 

 implies extinction. The genera Ornithorhynchus and Lepi- 

 (losiren, for example, woulil not have been less aberrant had 

 each been represented by a dozen species instead of by a single 

 one, or by one; or two. We can, I think, account for this fact 

 only by looking at aberrant groups as forms which have been 

 con([uered by more successful competitors, with a few mem- 

 bers still preserved under unusually favorable conditions. 



Mr. Waterhouse has remarked that, when a member be- 

 longing to one group of animals exhibits an alTinity to a cpiite 

 distinct group, this alVmity in most cases is general and not 

 special : thus, according to Mr. Waterhouse, of all Rodents, 

 the bizcacha is most nearly related to Marsupials; but in the 

 points in which it ajiproaches this order, its relations are gen- 

 eral, and not to any one marsupial species more than to an- 

 other. As \]ui jjoints of allinity are believed to be real and 

 not merely adaptive, they nnist be due, in accordance with our 

 view, to inheritance from a conunon ])rogenitor. Therefore we 

 must su])j)ose either that all Rodents, including the bizcacha, 

 branched olV from some ancient Marsupial, which will naturallv 

 have been more or less intermediate in character with respect 

 to id! existing Marsupials; or that both Rodents and Marsu- 

 jjials branched olV iVom a cominou progenitor, and that both 



