The Eolis has a head prolonged into a pair of tentacles which are active and as sensitive as antennæ. Another pair on the back have ten or twelve narrow plates twisted in a spiral round them; the eyes are at the base of these horns. The mouth contains horny jaws and a spiny tongue like a mere strap covered by numerous transverse plates armed with recurved spines not more than a sixth part the thickness of a human hair. Fig. 176 represents the tongue and some of the spines greatly magnified. The mouth leads into a short and large membranous stomach, from each side of which branches are sent off, from whence long canals traverse the papillæ longitudinally, and perform the part of a liver. In many species these tubes are brilliantly coloured, but none are more beautiful than those in the Eolis coronata, which is found under stones, like a mass of jelly, not larger than a pea, at low spring tides, on our own coasts. When put into sea-water it expands till it is about an inch long (fig. 175). It is then pellucid, tinged with pink, and the central tubes in its numerous papillæ are of a rich crimson hue, their surface reflects a metallic blue, and their tips are opaque white; as the animal keeps its papillæ in constant motion the effect is very pretty. The Eolis coronata, like all its congeners, has a stinging apparatus, consisting of an oblong bag, full of thread cells, placed at the extremity of each papilla, from whence darts can be ejected through an aperture in the tip. The whole of the Eolididæ are carnivorous, fierce, and voracious, setting up their papillæ like the quills of a porcupine when they seize their prey; they tear off the papillæ of their weaker brethren, and even devour their own spawn, though their chief food consists of zoophytes.