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Show 1905.] BEARING ACTINIANS IN THEIR CLAWS. 499 actinians at once makes it certain that the commensalism is not restricted to a single species of actinian, as might have been supposed ; moreover, the experiments given below- prove that the indrvidual crab will seize whichever of the two forms is presented to it. It may be, however, that the commensalism is limited to these two forms of actinians, Bunodeopsis and Sagartia. The figure of the actinian which Borradaile gives, reproduced 011 p. 496 (text-fig. 73), closely recalls the sagartiids found 011 the Hawaiian crabs, though he writes me that it is to be regarded as only a conventional representation. Richter's figure (p. 495, text-fig. 72) is clearly intended for a Bunodeopsis, and there is no reason to suppose that the form is different from the Hawaiian species. Experiments were first conducted to determine the responses of Melia toward different actinians. The first crab was deprived of both its bunodeopsids and then placed in a dish in which were the two sagartiids removed from the claws of the second crab, the polyps lying free upon the bottom of the dish, not fixed by their base. The crab walked about for some time, showing no response whatever which would indicate that it was aware of the presence of the actinians; many a time it would pass in close proximity to them without any recognition signs. Happening in its wanderings to touch one of the sagartiids, it stopped immediately, moved its claws around as if examining the polyp, and then grasped it at an oblique angle and carried it away. After the crab had moved about for some time longer, with one claw occupied and the other vacant, the second sagartiid was intentionally placed so as to touch the unoccupied chela, when it was likewise examined, seized upon, and carried off. ' Thus the crab which originally held two bunodeopsids had now provided itself with two sagartiids; hence the species of actinian as regards Bunodeopsis and Sagartia are interchangeable. One of the sagartiids was now released and placed in the dish along with its original crab having both chelipeds vacant, the bunodeopsid fragment being also introduced. After a short time the Sagartia was seized, and later the small fragment of Bunodeopsis. The first Melia was also placed in a dish along with its own Bunodeopsis and a Sagartia, and after a time these were likewise appropriated. Thus each crab was again provided with two actinians but of different species, the one a bunodeopsid and the other a sagartiid. In all the experiments the crabs appeared to seize either one or the other species with equal readiness. Experiments as to the behaviour of the crabs towards other species of actinians were very desirable, but at the time no other forms were available. The crabs exercised what must unquestionably be considered an intelligent selection, as far as regards the desirability or otherwise of an actinian already held by them. A Melia carrying a small fragment of a Bunodeopsis in one claw and a perfect Sagartia in the other was placed in a dish containing the full- |