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Locomotion

arms, move and tropiometra

LOCOMOTION.

Like most of the comatulids hitherto studied, Tropiometra is exceed ingly sluggish. So far as my observations go, it never swims. Dropped or suspended in deep water, it makes only the most feeble arm-move ments and, unless artificially prevented, it sinks rapidly to the bottom. When, as a result of some adequate stimulus, Tropiometra does move, the movement is similar to that of Comanthus. That is, it is accom plished solely by means of the arms, and no particular arms take pre cedence in the matter. In one respect the attitude differs from that of Comanthus, for the body is much more distinctly raised. This is obviously to keep the cirri wholly above the substratum and thus prevent their accidentally catching on it. The movement is always slow and labored and does not continue long. When overturned so that the cirri are up, a normal healthy Tropiometra invariably rights itself at once, sometimes only very slowly and deliberately, but usually without delay. The process is, as in other comatulids, by several arms raising up their side of the body until one or more of them or some of the neighboring arms can reach over backwards and secure a hold which will enable them to pull the body over. The cirri play

no part whatever in this process, any more than in actual locomotion ; they are very inert, move slowly and slightly, and are used only as organs of attachment, a purpose which they serve admirably. The pinnules, even near the tip of the arm, have only weakly hooked tips and are but slightly viscid, and it is consequently difficult for Tropio metro to move or even to right itself except on a rough and rather firm surface. No individuals were seen moving about under normal con ditions, but when placed on a bare, sandy bottom they crept steadily to its margin of coralline ape. Many specimens were planted on the reef-flat near the laboratory and most of these ultimately disappeared, but whether they crept away or were carried off by tidal movements it is impossible to say.