CHAPTER XXI. 



THE DISTRIBUTION OF SOME OF THE MOKE IMPORTANT FAMILIES 

 AND GENERA OF INSECTS. 



Although insects are, for tlie 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 tliey 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 Noctuidae, 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 fhing occurs, though perhaps in a less degree, 

 among the Coleoptera. While the Carabidse, Buprestidae, and 



