The ophiurans, or brittle-stars, differ from the starfishes in having the arms quite distinct from the body. In starfishes the arms are extensions of the body, and the viscera extend partway into them, while in ophiurans the body is a central disk, with the five narrow arms attached to its margin. In form they suggest a spider, and sometimes are called sea-spiders. The name brittle-star is also descriptive, since they break off their limbs readily. The arms are narrow, taper to a point, usually curl at the ends, and have no ambulacral grooves, but are completely covered with bare calcareous plates (except in the first order, where they have a skin and no plates). The ambulacra are small spines without suckers, which emanate from the sides or margins of the arms and do not serve for walking. The madreporic plate is on the ventral surface, in one of the circular shields which surround the mouth. The alimentary canal ends blindly. The egg-sacs lie between the arms and open by slits on the under side, close to the arms, where they join the disk. Water flows in and out of these pouches, which are thought to have also respiratory and excretory functions. No eye-specks have been found, but they must exist, since the animal is sensible to approaching danger and quickly retreats. The ophiurans are more active than starfishes, moving by wriggling, and clambering with their arms. They are shy and hard to find, and it is difficult to capture a whole one, since they throw off pieces of their arms at the least alarm. Often they completely dismember themselves, an action which does them no permanent injury, since they reproduce lost parts. They are more commonly inhabitants of deep than of shallow waters, and are brought up from the bottom in dredges in great numbers. [pg215] Some species may be found near low-water mark under stones and in clusters of mussels, and often in seaweeds, thrown up from deep water, on the shore. ORDER =EURYALIDA= GENUS ^Astrophyton^ (Plate LV.)