162 
ZOOLOGICAL GEOGRAPHY. 
[part III. 
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 trork 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 Regions 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 Palaearctic and Neurotic 
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 
