no fewer than eight zones of life, in the course of which the number and variety of forms gradually diminished; until, beyond 300 fathoms, life disappeared altogther. Hence it appeared as if descent in the sea had much the same effect on life as ascent on land. Recent investigations appear to show that Forbes was right enough in his classification of the facts of distribution in depth as they are to be observed in the Ægean; and though, at the time he wrote, one or two observations were extant which might have warned him not to generalize too extensively from his Ægean experience, his own dredging-work was so much more extensive and systematic than that of any other naturalist, that it is not wonderful he should have felt justified in building upon it. Nevertheless, so far as the limit of the range of life in depth goes, Forbes's conclusion has been completely negatived, and the greatest depths yet attained show not even an approach to a "zero of life:"

As Dr. Wyville Thomson's recent letter, cited above, shows, the use of the trawl, at great depths, has brought to light a still greater diversity of life. Fishes came up from a depth of 600 to more than 1,000 fathoms, all "in a peculiar condition from the expansion of the air contained in their bodies. On this relief from the extreme pressure, their eyes, especially, had a singular appearance, protruding like great globes from their heads." Bivalve and univalve mollusca seem to be rare at the greatest depths; but star-fishes, sea-urchins, and other echinoderms, zoophytes, sponges, and protozoa, abound.

It is obvious that the Challenger has the privilege of opening a new chapter in the history of the living world. She cannot send down her dredges and her trawls into these virgin depths of the great ocean