SENSE ORGANS.—The most widely diffused sense organs are the antennae or feelers, which may serve for touch or smell, or possibly both. Each antenna is a conical or tubular outgrowth of the skin; from its apex projects a fine pencil of sense hairs borne on a protoplasmic cushion, which receives a nerve. Often the antenna is elongated, and may then contain a muscle by which it is retractile (lateral antennae of _Melicerta_); sometimes it is reduced to a slight prominence bearing the setae (dorsal antenna of this genus). There are usually three antennae—a _median dorsal_ (Figs. 109, B, _a_, and 112, C, _am_) and two _lateral_ (Figs. 106, 112, C, and 115, A, _al_), often approximated towards the ventral surface, and sometimes all but fused on the middle line, or completely united (_Conochilus dossuarius_, _Copeus caudatus_).[259] Most Rotifers possess an organ of sight. This in its simplest form is a refractive globule seated in a red pigmented cup through which the nerve passes; in other cases it lies directly on the brain. Very frequently the eye is paired (Figs. 112, B, and 115, A); and these paired eyes may lie on the brain, and then {216}are so close together that the pigment-cups have the shape of an _x_, or else they are seated in the dorsal region of the head behind the disc. In some cases they lie just under the ciliary wreath, or even within the region of the disc, and pass towards its ventral side in _Pedalion_ (Fig. 117, A, _e_). In _Rotifer_ they lie just under the dorsal side of the proboscis just below its apex. The median and two lateral eyes often exist together, as in _Eosphora_; and sometimes additional paired eyes exist. In _Furcularia longiseta_, var. _grandis_ a pair of pigment spots (eyes?) occurs at the hinder end of the body just in front of the foot. The active Ploima show a spontaneity of movement and marked power of avoiding obstacles, etc. This is still more marked in the very active _Pedalion_, which, as Rousselet notes, clearly avoids capture by the dropping tube, aided by its sense of sight, as he suggests, or by the tactile or olfactory powers of the antennae. They must rank as psychically high in the scale of creatures of simple organisation.