There are as many polypites on the under-side of the bulb as there are red worm-like sacs on its upper edge. Each polypite consists of three distinct parts. The posterior part is a hollow red stalk inserted under the circumference of the disk; the second part is a bright yellow globular expansion containing the digestive cavity lined with cilia; the third and anterior part, which ends with the mouth, is quite colourless and transparent, and assumes various shapes by constant expansion and contraction. At the limit between the red stalk and the yellow globular part of the polypites there is a tuft of cylindrical appendages, from which a long tentacle descends with its secondary tentacles and red nettle-bulbs. All the canals of this Physophora are connected, and their walls are lined with muscular fibres, either circular, longitudinal, or both, which give a marvellous contractile and motive power. When the animal is suspended from the surface of the sea by its float, every member is in motion, especially the numerous tentacles, which are perpetually in search of food, and are so extremely sensitive that even a sudden motion of the water makes them shrink under the red worm-like organs on the edge of the disk. This animal is generally from one to three inches long. All the preceding members of the physograde group are really campanograde, for the action of the wind upon the floats of the Physophoridæ must be small, otherwise they would not be furnished with so many swimming cups. The Physaliidæ and Velellidæ are the only two orders that are truly physograde, for the wind is their only locomotive power. The Physalia, or ‘Spanish man-of-war’ of sailors, is by far the most formidable animal of the Acalephæ tribe; its poisonous stings, which burn like fire, inflict instant death on the inferior animals, and give painful wounds to man himself. Its body, as it floats, is a long horizontal double sac (fig. 121), which begins with a blunt point, gradually enlarges, and becomes cylindrical about the middle; then it somewhat suddenly widens in a transverse or lateral direction. Along the upper surface of the pointed half the membrane or wall of the sac is raised into a transversely placed crest, which dies away at the enlarged end. The greater part of the body is smooth, but the under-surface of the transversely enlarged end swells into lobes, from whence numerous tentacles and other organs descend.