DISTKIBUTION OF ORGANISMS. 229 



have possessed, as is likely from its distance, a different deve- 

 lopment of animal life from the Northern, and be supposed as 

 sending off terrestrial animals in like manner into South 

 America, the interposition of several great zones of different 

 climate stands forth as a sufficient reason why there should 

 not have been the same communication of zoological forms in 

 that case to the hyperborean seas, as there was from those 

 laving North America to those which dash upon Scandinavia, 

 Russia, and Siberia. 



The hypothesis is equally applicable to the imperfect deve- 

 lopments of life upon the more recently raised lands, such as 

 the Galapagos Islands and Australia. Development is a 

 matter of time, and in the case of these regions, the full time 

 has not yet elapsed. It is therefore exactly what we might 

 expect, upon the natural hypothesis, that, in these regions, 

 animal life should have yet hardly reached the mammalian 

 stage, the point which was attained in our elder and greater 

 province about the time of the oolite. 1 On the other hand, no 

 rational cause for this imperfect zoological show can be pre- 

 sented in consonance with the plan of special exertions. 



1 See this argument more fully elucidated in Explanations, a Sequel to 

 the Vestiges, &c. 



