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TROPICAL NATURE 
IX 
that each species inhabiting a country was specially adapted 
to the physical conditions that prevailed there, to which it 
was exactly fitted. Even if this theory had been true, it was 
an unproductive ultimate fact, for it was never pretended 
that we could discover any reason for the limitation of 
humming-birds and cactuses to America, of hippopotami to 
Africa, or of kangaroos and gum-trees to Australia ; and we 
were obliged to believe either that these countries possessed 
hidden peculiarities of climate or other conditions, or that 
this was only one out of many unknown and unknowable 
causes determining the special action of the creative power. 
All this was felt to be so unsatisfactory that the majority of 
naturalists openly declared that their sole business was to 
accumulate facts, and that any attempt to co-ordinate these 
facts and see what inferences could be drawn from them was 
altogether premature. In this frame of mind, year after 
year passed away, adding its quota to the vast mass of 
undigested facts which were accumulating in every branch of 
the science. The remotest parts of the globe were ransacked 
to add to the treasures of our museums, and the number of 
known species became so enormous that students began to 
confine themselves not merely to single classes, as birds or 
insects, but to single orders, as beetles or land-shells, or even 
to smaller groups, as weevils or butterflies. All, too, were 
so impressed with the belief in the reality and permanence of 
species, that endless labour was bestowed on the attempt to 
distinguish them — a task whose hopelessness may be inferred 
from the fact that, even in the well-known British flora, one 
authority describes sixty-two species of brambles and roses, 
another of equal eminence only ten species of the same 
groups ; and it is by no means uncommon for two, five, or 
even ten species of one author to be classed as a single 
species by another. All this time geologists had been so 
assiduously at work in the discovery of organic remains that 
the extinct species often equalled, and, in some groups — 
as the Mollusca — very far exceeded, those now living on the 
earth, and these were all found to belong to the very same 
classes and orders as the living forms, and to form part of 
one great system. Much attention was now paid to the 
geological succession of the different groups of animals, which 
