The Brachion has four longitudinal muscular bands transversely striated, which move the ciliated lobes of the head, push them out and draw them in. From these muscular threads are sent to the different parts of the body, to the mouth especially, two strong bands, which bend and unbend the joints of the hammer-like jaws. The vigorous motions of the long serpentine foot and the firm hold of its anchors are owing to muscular bands fixed high up on the interior wall of the body, which extend throughout the whole length of the flexible organ. As long as the Brachion is fixed, the vibrations of the cilia on its lobes only produce whirlpools in the water, but the moment that it lets go its hold, these vibrations, in consequence of the reaction of the water, give the animal both a smooth progressive motion and a rotation round its axis. Minute as the Brachionus pala is, it has several organs of sense. A sparkling, ruby-coloured, square eye-speck with a crystalline lens and crimson pigment layer is placed on a wart-like prominence on its back, and this prominence Mr. Gosse believes to be the brain of the animal. In the cleft between the spines and close to the eye-speck are two tubes, one within the other. The innermost tube, which can be protruded and withdrawn, has a bunch of bristles at its extremity that have the sensibility of antennæ. Nerves from the brain pass into these, to the various organs of the body, and to the lobes on the head. The Brachion has no propelling vessel or heart to maintain the circulation of its liquids, but, like the Annelids, a colourless liquid occupies the general cavity between the alimentary canal and the internal wall of the body. It is believed to be connected with nutrition, and is furnished with oxygen by a complicated organism, and is kept in motion by the vibrations of long cilia. The determination of the whole structure and motions of a creature barely visible to the naked eye, is a wonderful instance of microscopic research, and of the perfection of the mechanism exhibited in the most minute objects of creation. [Illustration: Fig. 137. Common Rotifer:—_a_, mouth; _b_, eye-spots; _c_, wheels; _d_, probably antenna; _e_, jaws and teeth; _f_, alimentary canal; _g_, glandular mass enclosing it; _h_, longitudinal muscles; _i_, tubes of water-vascular system; _k_, young animal; _l_, cloaca.] Fig. 137 represents the common Rotifer when its wheels are expanded and when they are retracted. The body is slender and flexible, it is stretched out by longitudinal muscles, and its girth is diminished by circular ones. The internal structure is similar to that of the Brachion, but there is a prominence or head between the wheels on which there are two crimson eye-specks, and the foot terminates in three concentric movable tubes that can be protruded and drawn in like the tubes of a telescope; each has a pair of claspers to enable the Rotifer to fix itself to any object.