ablished regions; others looked upon eventual agreements
as their final corroboration, especially when for instance such diverse
groups as mammals and scorpions could, with some ingenuity, be made to
harmonise. But the obvious result of all these efforts was the growing
knowledge that almost every class seemed to follow principles of its
own. The regions tallied neither in extent nor in numbers, although
most of them gravitated more and more towards three centres, namely
Australia, South America and the rest of the world. Still zoologists
persisted in the search, and the various modes and capabilities of
dispersal of the respective groups were thought sufficient explanation
of the divergent results in trying to bring the mapping of the world
under one scheme.

Contemporary literature is full of devices for the mechanical dispersal
of animals. Marine currents, warm and cold, were favoured all the
more since they showed the probable original homes of the creatures in
question. If these could not stand sea-water, they floated upon logs or
icebergs, or they were blown across by storms; fishes were lifted over
barriers by waterspouts, and there is on record even an hypothetical
land tortoise, full of eggs, which colonised an oceanic island after a
perilous sea voyage upon a tree trunk. Accidents will happen, and beyond
doubt many freaks of discontinuous distribution have to be accounted
for by some such means. But whilst sufficient for the scanty settlers of
true oceanic islands, they cannot be held seriously to account for the
rich fauna of a large continent, over which palaeontology shows us that
the immigrants have passed like waves. It should also be borne in mind
that there is a great difference between flotsam and jetsam. A current
is an extension of the same medium and the animals in it may suffer no
change during even a long voyage, since they may be brought from one
litoral to another where they will still be in the same or but slightly
altered environment. But the jetsam is in the position of a passenger
who has been carried off by the wrong train. Almost every year some
American land birds arrive at our western coasts and none of them have
gained a permanent footing although such visits must have taken place
since prehistoric times. It was therefore argued that only those groups
of animals should be used for locating and defining regions which were
absolutely bound to the soil. This method likewise gave results not