162 ZOOLOGICAL GEOGRAPHY. [PART m. 



various means of dispersal of , the different groups, and the 

 comparative longevity of their species and genera. Even insects, 

 which are perhaps of all animals the farthest removed from 

 mammalia in this respect, agree, in the great outlines of their 

 distribution, with the vertebrate orders. The Eegions are 

 admittedly the same, or nearly the same for both ; and the 

 discrepancies that occur are of a nature which can be explained 

 by two undoubted facts the greater antiquity, and the greater 

 facilities for dispersal, of insects. 



But this principle, if sound, must be carried farther, and be 

 applied to plants also. There are not wanting indications that 

 this may be successfully done; and it seems not improbable, 

 that the reason why botanists have hitherto failed to determine, 

 with any unanimity, which are the most natural phytological 

 regions, and ~to work out any connected theory of the migra- 

 tions of plants, is, because they have not been furnished with 

 the clue to the past changes of the great land masses, which 

 could only be arrived at by such an examination of the past 

 and present distribution of the higher animals as has been 

 here attempted. The difficulties in the way of the study of 

 the distribution of plants, from this point of view, will be 

 undoubtedly very great ; owing to the unusual facilities for 

 distribution many of them possess, and the absence of any 

 group which might take the place of the mammalia among 

 animals, and serve as a guide and standard for the rest. We 

 cannot expect the regions to be so well defined in the case of 

 plants as in that of animals ; and there are sure to be many 

 anomalies and discrepancies, which will require long" study to 

 unravel The Six Great Eegions here adopted, are however, as 

 a whole, very well characterised by their vegetable forms. 

 The floras of tropical America, of Australia, of South Africa, and 

 of Indo-Malaya, stand out with as much individuality as do 

 the faunas; while the plants of the Palsearctic and Nearctic 

 regions, exhibit resemblances and diversities, of a character not 

 unlike those found among the animals. 



This is not a mere question of applying to the vegetable king- 

 dom a series of arbitrary divisions of the earth which have been 



