The luxuriant vegetation, both attached and floating, and varying from giant kelp, scores of feet in length, to microscopic algae which an amoeba might encompass, clothes the surface of the continental shelf except in unfavourable localities or is carried here and there by the currents moving over it, but has its lower limit at about the 100-fathom line. This inferior limit of marine vegetation is probably more definitely defined than the superior limit of land plants on snow-capped mountains. All attached seaweeds are confined to the shallow seas, but floating kelp, like the well-known Gulf weed or sargasso, which collects in the eddies of the sea currents and forms more or less mythical floating islands, is widely distributed, as are also many kinds of minute algae which thrive in the upper 100 fathoms of the open ocean in all latitudes. The primary source of food for the hungry millions of marine animals, excepting the comparatively small quantity brought by rivers or blown from the land, is supplied by the marine algae, and mainly by the minute forms which float in the water. So much space has just been given to the marvellous luxuriance of life on the southern portion of the great shelf surrounding North America that the reader may perhaps think the cold northern oceans are even more lifeless and desolate than their adjacent shores. This, however, is not the case. Northward along the continental shelf, with decrease in the strength of the sunlight, the plants and animals lose much of the brilliancy which characterizes many of the denizens of southern waters, and in general assume more subdued colours in harmony with the prevailing gray of their surroundings. The great diversity of animal life to be found in shallow tropical seas decreases as one traces the continental shelf northward, but even in the Arctic Ocean adjacent to the land invertebrate life literally swarms, although the number of species, genera, etc., is comparatively limited. Seaweeds are not absent from the Arctic Ocean, although its shores, owing to the destructive action of ice, usually seem exceedingly barren, and the lower or smaller forms of algae float in the waters in abundance. Food sufficient for an extensive fauna is thus supplied, and where food is plentiful animals are present also, no matter what the mean annual temperature may be. The life of the Arctic Ocean has been but inadequately studied, but enough is known concerning it to show that a promising field there awaits the naturalist. On the continental shelf off Point Barrow, the most northern portion of the arctic shore of Alaska (latitude 71 deg. 23'), 180 species of marine invertebrates have been collected. Of these, the molluscs numbered 61 species; the crustaceans, 44 species; the worms, 20 species; and the echinoderms (sea-urchins, starfish, etc.), 17 species.