Chap. XIV.] OEGANIC BEINGS. 227 



conquered by more successful competitors, with a few 

 members still preserved under unusually favourable 

 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. Water- 

 house, of all Eodents, the bizcacha is most nearly related 

 to 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 be due in accordance with our view 

 to inheritance from a common progenitor. Therefore 

 we must suppose either that all Eodents, including the 

 bizcacha, branched off from some ancient Marsupial, 

 which will naturally have been more or less intermediate 

 in character with respect to all existing Marsupials ; or 

 that both Eodents and Marsupials branched off from a 

 common progenitor, and that both groups have since 

 undergone much modification in divergent directions. 

 On either view we must suppose that the bizcacha has 

 retained, by inheritance, more of the characters of its 

 ancient progenitor than have other Eodents ; and there- 

 fore it will not be specially related to any one existing 

 Marsupial, but indirectly to all or nearly all Marsupials, 

 irom having partially, retained the character of their 

 common 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 Eodents. In this case, however, it may be strongly 

 suspected that the resemblance is only analogical, owing 



