CLASSIFICATION 237 



anc-ieiit progenitor than have other Rodents; and there- 

 fore it will not be specially related to any one existing 

 Marsupial, but indirectly to all or nearly all Marsupials, 

 from having partially retained the character of their com- 

 mon progenitor, or of some early member of the group. 

 On the other hand, of all Marsupials, as Mr. Waterhouse 

 has remarked, the Phascolomys resembles most nearly, 

 not any one species, but the general order of Rodents. 

 In this case, however, it may be strongly suspected that 

 the Tesemblance is only analogical, owing to the Phas 

 colomys having become adapted to habits like those of a 

 Rodent. The elder De Candolle has made nearly similar 

 observations on the general nature of the affinities of dis- 

 tinct families of plants. 



On the principle of the multiplication and gradual 

 divergence in character of the species descended from a 

 common progenitor, together with their retention by in- 

 heritance of some characters in common, we can under- 

 stand the excessively complex and radiating affinities by 

 which all the members of the same family or higher 

 group are connected together. For the common progen- 

 itor of a whole family, now broken up by extinction 

 into distinct groups and sub-groups, will have transmitted 

 some of its characters, modified in various ways and de- 

 grees, to all the species; and they will consequently 

 be related to each other by circuitous lines of affinity 

 of various lengths (as may be seen in the diagram so 

 often referred to), mounting up through many predeces- 

 sors. As it is difficult to show the blood-relationship 

 between the numerous kindred of any ancient and noble 

 family even by the aid of a genealogical tree, and almost 

 impossible to do so without this aid, we can understand 



