The various internal organs of a Rotifer are readily seen through its transparent skin (Fig. 34, A). It has a nervous system, many bands of contractile muscles and a pair of little tubular kidneys or nephridia, besides reproductive germs (the eggs). I have here sketched only the digestive canal. The mouth leads through a gullet to a very curious organ called the "gizzard," marked G. All the wheel animalcules have this gizzard, but its teeth, shown as two oval bodies in the drawing, differ a great deal in shape and complexity in the different kinds. Whilst the Rotifer is feeding by bringing currents of water to its mouth, the two halves of the gizzard are kept in rapid movement by muscles, causing them to rub against one another and to grind up the food particles which reach them through the gullet. The gizzard (G) is followed by the digestive stomach (St), and that by the intestine (Int), which opens at the vent (V). The side (or three-quarter profile) view of a similar specimen (Fig. 34, B) shows only the surface of the little animal, and is intended to show especially the snout-like head-lobe (S), with its two eye-spots, which are red in colour. Standing out backwards from this is a finger-like process (T), which is called the spur, or tentacle. It has hairs at its tip, and is a sensory organ. [Illustration: FIG. 35.–The Rotifer _Pedalion mirum_–seen from the right side, magnified 180 diameters. _w.a._, wheel apparatus or "ciliated" margin of the cephalic disc. _r.e._, right side eye-spot. _m._, mouth. _p._, tactile process. _d.l._, median dorsal limb (as it is seen in profile, only three of the fringed hairs at its extremity are seen). _v.l._, the great ventral limb (only five of its fan of eight fringed hairs are seen). _l.l._^1, dorso-lateral, and _l.l._^2, ventro-lateral limbs of the right side: they show the complete fans of eight fringed hairs. _x._, the pair of posterior processes tipped with vibratile cilia, better seen in Fig. 36.] [Illustration: FIG. 36.–The Rotifer _Pedalion mirum_–seen from the ventral surface. Letters as in Fig. 35. The complete fan of eight fringed hairs terminating the great ventral limb are seen, and the three spine-like processes on each side of it. The fringed hairs of the two ventro-lateral limbs, _l.l._^2, are omitted; they are fully shown in Fig. 35, and are the same in number and disposition as those forming the "fan" of the great ventral limb. Compare these hairs with those of the "Nauplius" Crustacean larva drawn as a tail-piece to Chapter XIII.]