The science of life : fully illustrated in tone and line and including many diagrams

THE EVIDENCE FROM LIVING THINGS

speech. On this score the Galapagos and St. Helena and other oceanic -islandsislands, that is to say, of volcanic origin, which are separated by many miles of deep water from the continents, and apparently have never had any connection with the mainland—have much to tell us.

If different animals were created and placed in the countries best suited to them, why is it that oceanic islands never possess more than a sprinkling of landanimals and birds and flowering plants, and never any amphibians or land-mammals (except sometimes the too-readily _ transportable mice)? It is emphatically

not because such animals are unsuited to life on

islands, for rabbits and goats, cats and frogs thrive well enough when introduced, and often so much too well that they become a pest.

But if the distribution of living things is the result of evolution and migration, the reason is plain. It will never be easy for such isolated patches of earth to be colonized by life at all ; only those forms with

fly, only one land-animal—a rat, which may very likely have been introduced by the Maoris. It is separated from the rest of the continents by such distances, and has been separated for so long a time, that its animal population, at the time of its discovery, was in most ways like that of a real mid-ocean volcano. Yet all the time it was most admirably suited to support those very forms of life whichitlacked. The zeal of its acclimatization societies has stocked it with all kinds of European birds and animals and plants, many of which have found the country so much to their liking that they have become most abundant nuisances. Finally, we have a third set of facts, the facts of discon-

tinuous distribution, when, almost identical animals

are found only in = two or three widely separate regions of the world’s surface. Why in the name of all that is reasonable are tapirs found only in South America and Malaya ? Why is one branch of the camel family, the camels themselves, found only in Asia and North

remarkable powers of Africa, while the other, dissemination by air or the llamas and their kin, water will reach them. grows only in South Land-mammals and am- Fig. 148. The regions inhabited by America? Why are the phibians have notoriously Tapirs are shown stippled. Four lung-fish found only in

poor powers of dispersal ; they cannot survive long exposure to salt water, nor have they any resistant stage in their life-history which can either be blown on the wind like the spores of lower plants, or resist salt water like the seeds and fruits of some higher plants.

The same reasoning applies to New Zealand. New Zealand is not volcanic like true oceanic islands, but it includes only one amphibian and, apart from bats which can

im Malaya. wide separation ?

Species are found in South America and a

(The 1o0-fathom line is indicated as well as the coast-line.)

Australia, tropical South

isti ) ri ad tropical

fifth with characteristic coloration (below) America; an Vhat is th on for this Africa? Here geology ee solves our riddle. The

discontinuity did not always exist: the type was once widespread, but to-day has been exterminated save in a few patches. Lung-fish were among the most abundant_of fishes in Devonian (III D) and Carboniferous (III E) times, and were then spread over the whole world ; the competition of later-evolved and more efficient fish extinguished almost all of

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