This protective feature is a characteristic of life among the kelp forests that line the entire Pacific shores of North and South America, many animals simulating it so perfectly in color that the best-trained eyes often fail to observe them. This is especially true of the crabs and shell-less mollusks. The latter have not only assumed the exact tint of the weed, but are often covered with barbels of flesh that simulate the tangles of the substance. Upon the backs of the crabs are singular markings in green and white, which so resemble the minute incrustations of the kelp that the resultant protection is complete. [Compare illustration on page 252.] Each vine is fastened to a stone, and the clinging roots shelter hordes of creatures of various kinds—deep-water crabs, octopods, starfishes, and a host of others. [Illustration: A MARINE NATURALIST.] CHAPTER XIII ANIMAL LIFE IN THE SEA The primitive idea of the ocean was that it was a vast desert, and a strange disbelief in its being inhabited by more than the very few forms that everybody was compelled to recognize persisted up to quite modern times among those who should have known better. Pliny boldly asserted, for example, that nothing remained in the Mediterranean Sea unknown to him after he had made a list of 176 marine animals! But now we know that the sea teems with living beings as densely as do the fresh waters or the air. In it began the life of the globe, for the fossil records of the rocks show that the first animals lived in the ocean, and that ages passed before any of them began to people the newly formed lands and breathe the atmosphere instead of the air in the water; and, abundant as oceanic life now is, the paleozoic seas held immensely greater hordes, of which many forms were giants as compared with those of our day. Some of the old straight chambered shells were twelve feet long; and I have seen fossil ammonites, extinct relatives of our coiled pearly nautilus, which when alive must have been too heavy for a man to lift. The fishes, too, could tell great stories of the glory of their ancestors in size and strength and numbers. Some of them wore solid coats of mail upon their heads, and could do battle even with the huge swimming reptiles that were the dreaded tyrants of the Mesozoic deep. Life in the ocean in those old geologic days was a long guerrilla warfare—every animal guarding against attack, and at the same time watching sharply for an opportunity to seize and prey upon some weaker companion. As for the foraminifers and other microscopic creatures, they were countless, and their skeletons, singly invisible, have by accumulation built up great masses of rock, like the chalk-beds of England and France.