74 EXPLANATIONS. 



the grades of organization are not determinate in 

 this respect, but may be reached by steps of un- 

 equal length. Thus, for example, the marsupials 

 appear very clearly a development from certain 

 birds ; probably the rodent, edentate, and insec- 

 tivorous orders are derived through the same chan- 

 nel. In short, the progress of animality in the 

 different stirpes has been attended by peculiarities 

 which evidently affix peculiar characters to each, 

 and make the idea of a difference in time not only 

 probable, but unavoidable. 



Regarding the animal kingdom simply as a 

 combination of independent stirpes, each with its 

 distinct affinities, the theory of transmutation puts 

 on a totally new aspect ; so truly is this the case, 

 that transmutation is hardly any longer a term 

 approjDriate to the idea. The difficulty of suppos- 

 ing such changes as that from the rodent to the 

 ruminant, or the carnivorous animal to the quadru- 

 mane, vanishes, leaving only transitions from ove 

 form to another of a series generally similar — from 

 the otary, for instance, to the otter, fr'om certain 

 phocae to the bear, and so on. There is a unity 

 in all instances in the moral as well as physical 

 characters of the various members of one stirps ; 

 we only see it advancing from low to high charac- 



