In Fig. 34 I have sketched the common Rotifer or wheel animalcule. It is about the one-fortieth of an inch long. The two specimens drawn in Figs. 34, A and B, are seen to be clinging by the forked tail-end of the body to a piece of weed (drawn in dotted lines). The body is stretched in these specimens to its full length. It can be shortened by a "telescoping" or pulling in of either end, so as to make the animal a mere oval particle. The four narrower joints or segments at the tail-end can be pulled in like the segments of a telescope, whilst the two wheels and adjacent parts can be drawn down into the body as shown in Fig. 34, C, where the two wheels (W) are seen showing through the skin by transparency. [Illustration: FIG. 34.–Diagram of _Rotifer vulgaris_–the common wheel animalcule–one hundred and twenty times as long as the creature itself. _A_, front view. _B_, side view. _C_, head showing eyes _S_, and retracted wheel apparatus _W_. The letters in _A_ and _B_ have the following signification: _M_, mouth. _W_, wheel or ciliated disc. _S_, eye spots on head. _T_, spur or tentacle. _G_, gizzard. _St_, stomach. _Int_, intestines. _V_, vent: aperture of intestine.] The common rotifer can walk like a looping caterpillar or a leech–fixing itself by its tail, then stretching out the head and fixing that, whilst letting go the tail and bringing it up by "telescoping" it, near to the head region. The tail is forked, and in the side view (Fig. 34, B) it is seen to have a soft branched process, which helps it to cling. The letter V in Fig. 34, A, points to the vent or opening of the gut at the fork of the tail. The mouth, marked M, is seen between the two "wheels." The two "wheels" are really two discs, the edges of which are beset by coarse "cilia," or vibrating hairs of protoplasm.[5] These cilia "lash" and straighten again one after the other, so that the optical illusion is produced of the toothed edge of the disc being in movement like a wheel. They may be "focused" with the microscope so that the groups or "bunches" of them look like stiff, motionless "teeth," although they are really, all the time, lashing and beating in regular rhythm. When the animal is fixed by its tail, the lashing of the cilia on the wheels causes currents in the water which set with great strength to the mouth and bring floating food particles to it. It is thus that the Rotifer feeds. When the tail is not grasping a support, the movement of the cilia on the wheels causes the animal to swim forward through the water, so that it has two modes of locomotion–the leech-like crawling method and the free swimming method.