The sterile polypites that are attached at intervals by their hollow stems to the twisted body of the Apolemia, have twelve rows of cells inserted in the bright lining of their digestive cavities; their anterior part has a trumpet-shaped mouth full of thread-cells. The tentacles affixed to their stems and their secondary lines are like those of the Diphyidæ. Besides these sterile polypites, which serve only to feed the animal, the Apolemia has a kind of mouthless prolific organs, which do not contribute to the general nourishment: each group has a pair of them attached to the extremity of a branching stem. They resemble polypites in being long and contractile at their extremities; the interior is full of a substance like sarcode, and encompassed by a red ring. Female buds yielding eggs appear on the stem of one of these organs, while male buds are developed into medusiform zooids on the stem of the other, which become detached, swim away, and the fertilized eggs yield young Apolemiæ. The natural position of an individual of the family of the Physophoridæ when at rest is to hang perpendicularly from its air-vessel. The body, which begins with a pyriform float, descends in a slender filiform scarlet tube with a number of hyaline natatory cups or bells attached on each side. The lower end of the body enlarges into a bulb or disk supporting various appendages. The Physophora hydrostatica (fig. 120), common in the Mediterranean, has a transparent pear-shaped air-vessel tipped with red, from which the slender cord-like tube of the body descends. Immediately below the air-vessel, a number of buds and young bells are attached, followed by a series of perfect three-lobed swimming bells, placed on each side obliquely one below the other; and as they alternate and embrace the body with their deeply excavated sides, they give it the appearance of a crystal cone. Four canals spring from the hollow stalks of the bells, traverse them, and end in a circular canal close to the membranaceous iris which surrounds the margin of the internal cavity. Below the cone the tubular body expands, and is twisted into a flat spiral, so as to form a hollow disk or bulb, to which three different circlets of organs are appended. The first and uppermost is a coronet of red, worm-like, closed sacs, in constant motion, with large thread-cells at their pointed extremities. They are attached to the upper surface of the bulb by their broad bases, and communicate with its tubes by a small valve. Male and female capsules follow either in a circle, or mixed with the third and undermost circlet of organs, which consist of sterile nourishing polypites, fixed by hollow stems to the bulb, each of which has a long branching tentacle fixed to the base of its digesting cavity.