New Discoveries Concerning the Octopus. 25

sia particularly, interested him. He found it feeding on the sea-weed, and when disturbed it emitted the peculiar purple fluid for which it is noted. The pools of water left by the outgoing tide formed aquaria of more than ordinary interest. The octopus was the subject of many observations, numbers of which were seen clinging to the rocks by their eight sucker-lined arms, or dashing across the pool, ejecting the cloud of ink which constitutes a part of their defence.

The young naturalist was quick to note their power of mimicry, a fact in this and other animals that was dwelt upon in later years by himself and Wallace. He noticed that they changed their tints according to the ground over which they passed, and a close examination showed that clouds of colour were continually passing over them, varying from hyacinth-red to chestnut-brown in tint.

Darwin was probably the first to apply a galvanic battery to these beautiful creatures, with the result that the part touched became almost black. He noticed that they changed colour under all circumstances, whether swimming or resting, and was the first to call attention to the fact that the ink was used as a means of concealing the direction of retreat. One cuttle-fish in this natural aquarium ejected water above the surface from a hole in which it lay concealed, and he suspected that it could direct its aim by turning its tube or siphon in a given direction. Whether this is true or not would be difficult to ascertain, but the author has seen a squid force its stream of ink a foot or more

above the surface, striking an inquisitive observer full in the face.

Darwin was perhaps the first also to observe that the octopus is luminous at times. One which he kept in his cabin gleamed with a slight phosphorescence, which we can imagine might be used as a decoy, or perhaps to menace its foes.

In February, 1831, the Beagle sighted the famous St. Paul's Rocks, one of the most desolate spots on the globe, consisting of a few rocks five hundred and forty miles from the American coast and three hundred and fifty from Fernando de Noronha. The rocks are somewhat difficult to find, as they rear themselves but fifty feet above the sea and are but little over three-quarters of a mile in circumference. From a distance they appear white, from the constant presence of vast numbers of birds which have made the location their roosting-place for generations.

The birds, principally the noddy and tern, were so tame that any number could have been killed by hand. They laid their eggs on the rocks where the sun hatched the young. Desolate as the spot was, warfare existed; the parent birds provided the young with small fish for food, the flying-fish being considered an especial dainty; but no sooner was it placed by the nest than the young naturalist, who was concealed behind some rock, saw a handsomely mottled crab the Grapsus-come slowly up, edging along in an innocent, disinterested fashion, then suddenly when within reach seize the fish and dash away.