It is obvious that between the dredge, the trawl, and the tangles, there is little chance for any organism, except such as are able to burrow rapidly, to remain safely at the bottom of any part of the sea which the Challenger undertakes to explore.  And, for the first time in the history of scientific exploration, we have a fair chance of learning what the population of the depths of the sea is like in the most widely different parts of the world.

And now arises the next question.  The means of exploration being fairly adequate, what forms of life may be looked for at these vast depths?

The systematic study of the Distribution of living beings is the most modern branch of Biological Science, and came into existence long after Morphology and Physiology had attained a considerable development.  This naturally does not imply that, from the time men began to observe natural phenomena, they were ignorant of the fact that the animals and plants of one part of the world are different from those in other regions; or that those of the hills are different from those of the plains in the same region; or finally that some marine creatures are found only in the shallows, while others inhabit the deeps.  Nevertheless, it was only after the discovery of America that the attention of naturalists was powerfully drawn to the wonderful differences between the animal population of the central and southern parts of the new world and that of those parts of the old world which lie under the same parallels of latitude.  So far back as 1667 Abraham Mylius, in his treatise “De Animalium origine et migratione, populorum,” argues that, since there are innumerable species of animals in America which do not exist elsewhere, they must have been made and placed there by the Deity:  Buffon no less forcibly insists upon the difference between the Faunae of the old and new world.  But the first attempt to gather facts of this order into a whole, and to coordinate them into a series of generalizations, or laws of Geographical Distribution, is not a century old, and is contained in the “Specimen Zoologiae Geographicae Quadrupedum Domicilia et Migrationes sistens,” published, in 1777, by the learned Brunswick Professor, Eberhard Zimmermann, who illustrates his work by what he calls a “Tabula Zoographica,” which is the oldest distributional map known to me.

In regard to matters of fact, Zimmermann’s chief aim is to show that among terrestrial mammals, some occur all over the world, while others are restricted to particular areas of greater or smaller extent; and that the abundance of species follows temperature, being greatest in warm and least in cold climates.  But marine animals, he thinks, obey no such law.  The Arctic and Atlantic seas, he says, are as full of fishes and other animals as those of the tropics.  It is, therefore, clear that cold does not affect the dwellers in the sea as it does land animals, and that this must be the case follows from the fact that