CHAPTER XXL 
THE DISTRIBUTION OF SOME OF THE MORE IMPORTANT FAMILIES 
AND GENERA OF INSECTS. 
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Althouch insects are, for the most part, truly terrestrial animals, 
and illustrate in a very striking manner the characteristic pheno- 
mena of distribution, it is impossible here to treat of them in 
much detail. This arises chiefly from their excessive numbers, 
but also from the minuteness and obscurity of many of the 
groups, and our imperfect knowledge of all but the European 
species. The number of described species of insects is uncertain, 
as no complete enumeration of them has ever been made ; but 
it probably exceeds 100,000, and these may belong to some- 
where about 10,000 genera — many times more than all verte- 
brate animals together. Of the eight Orders into which Insects 
are usually divided, only two — the Coleoptera and Lepidoptera 
— have been so thoroughly collected in all parts of the globe 
that they can be used, with any safety, to compare their distri- 
bution with that of vertebrate animals ; and even of these it is 
only certain favourite groups which have been so collected. 
Among Lepidoptera, for example, although the extensive group 
of Butterflies may be said, in a general sense, to be thoroughly 
well known — every spot visited by civilized man having fur- 
nished its quota to our collections — yet the minute Tineidse, or 
even the larger but obscure Xoctuidee, have scarcely been col- 
lected at all in tropical countries, and any attempt to study 
their geographical distribution would certainly lead to erroneous 
results. The same thing occurs, though perhaps in a less degree, 
among the Coleoptera. While the Carabidse, Buprestidse, and 
