The Physaliæ, which far surpass the Velellæ in size and beauty, are also inhabitants of the warmer seas, where the _Physalia caravella_, or "Portuguese man-of-war," is the mariner's admiration. On a large float-bladder eight or nine inches long and three inches broad, whose transparent crystal shines in every shade of purple and azure, rises a vertical comb, the upper border of which sparkles with fiery red. This beautiful float has a small opening at either end, and strong muscular walls, so that by their contraction its cavity can be considerably diminished. And thus partly by the escape of air forced out through the openings, and partly by the compression of what remains, the specific gravity is so much altered as to admit of the animal's sinking into the deep when danger threatens. Numerous polyps proceed from the lower surface, accompanied by tentacles having a sac-like extension at their base, and hanging down in beautifully blue and violet coloured locks or streamers. When fully extended, these tentacles form fishing lines fifteen or sixteen feet long, which, as their thread-cells are uncommonly large, at once paralyse the resistance of the fish or cephalopod they meet with. Then rolling together, they convey the senseless prey to the numerous mouths of the compound animal, which, sucking like leeches, pump out its nutritious juices. In this manner the greedy physalia devours many a bonito or flying-fish of a size far superior to its own, and such is the corrosive power of its tentacles that even man is punished with excruciating pains when heedlessly or ignorantly he comes within their reach. "One day," says Dutertre in his "History of the Antilles," "as I was sailing in a small boat, I saw a physalia, and as I was anxious to examine it more closely, I tried to get hold of it. But scarcely had I stretched out my hand when it was suddenly enveloped by a net of tentacles, and after the first impression of cold (for the animal has a cold touch) it seemed as if my arm had been plunged up to the shoulder in a caldron of boiling oil, so that I screamed with pain." In his journey round the world, Dr. Meyen also relates the case of a sailor who jumped overboard to catch a physalia. But scarce had he come within reach of its tentacles when the excruciating pain almost deprived him of sensation, and he was with great difficulty hauled out of the water. A severe fever was the consequence, and his life was for some time despaired of. Several of the Physophoridæ are provided, besides the float, with swimming-bells (_nectocalyces_) and peculiar appendages or bracteæ (_hydrophyllia_), which, overlapping the polypites, serve for their protection. The graceful _Athorybia rosacea_ possesses from twenty to forty of these organs inserted in two or three circlets immediately below the pneumatocyst, and above a much smaller number of polypites. It has the power of alternately raising and depressing them so as to render them agents of propulsion.