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Show 1905.] BEARING ACTINIANS IN THEIR CLAWS. 501 are sometimes thus deeply constricted and indented, and in one instance the body of the polyp was actually pierced by the two sharp points of the claws coming together. In such cases, it is conceivable that the crab when placed in preservative fluid had closed its chelse more firmly than usual. Under ordinary circumstances, the actinians do not seem to be in any way injured by the crab. Indeed, the polyps show no signs of their peculiar position being even one of irritation; shortly after seizure they expand to their full degree and remained in this condition, the tentacles outstretched and overhanging. Numerous observations with the crabs deprived of the polyps lead one to suppose that the actinians are encountered only in a haphazard manner, and also that the crab makes no response to their presence until it comes into actual contact with them. When the crabs with their claws unoccupied were placed in vessels along with free polyps, they would remain still or wander around in an apparently aimless manner, even coming close to the polyps without showing any signs of recognition. When, however, the chelipeds happened to touch a polyp the crab would at once stop, move its chelfe around the polyp for a few seconds, and then open the claws and seize hold of it in almost any position, not necessarily across the column. In their natural condition, most actinians are firmly adherent by a broad base to some substratum from which they are with difficulty dislodged ; and a priori it is not manifest how the crabs are able to detach and carry away a polyp thus firmly fixed. Faurot *, who has studied the habits of various Hermit Crabs (Pagurus) and their commensal actinians, Sagartia parasitica and Aclamsia palliata, finds that when a Hermit Crab attempts to remove a fixed actinian it seizes it with its maxillipeds and ambulatory limbs, and moves these about as if resisting the escape of some prey. These movements being continued bring about the retraction of the polyp, and in the end the detachment of its pedal disc from the surface of the glass or stone. Buno-deopsids and sagartiids have each adherent bases, and experiments were made to determine the manner in which they are loosened by the crustacean. After removal from the chela; the sagartiids failed to fix themselves, but remained lying free on their sides; the large Bunodeopsis, on the other hand, readily fixed itself to the bottom of the glass vessel, to such a degree that it was not detached by a strong stream of water from a pipette. A Melia with empty claws was then introduced into the vessel. In time the crab came into touch with the fixed actinian and began, as usual, to pass its chela* around it, but without effecting its dislodgment. Then the right member of the first pair of ambulatory appendages was brought forward, and its sharp end was applied between the polypal base and the surface of the glass, exactly in the manner one would apply one's finger in attempting to * Fauvot, L . : " Etudes sur l'anatomie, l'histologie et le developpement des Actinies," Arch de Zool. Exp. et Gen. 3 ser. vol. iii. p. 152. |
