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 

 individual 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 on 

 p. 496 (text-fig. 73), closely recalls the sagartiids found on 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 Bunodeojjsis, and there is 

 no reason to suppose that the form is dififerent from the Hawaiian 

 species. 



Experiments were first conducted to detei-mine the responses 

 of Melia toward diffei'ent actinians. The first crab was deprived 

 of both its bunodeopsids and then placed in a dish in which were 

 the two sagai'tiids 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 w^alked 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 wan- 

 derings 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, wdth one claw 

 occupied and the other vacant, the second sagartiid was inten- 

 tionally placed so as to touch the unoccupied chela, when it was 

 likewise examined, seized upon, and cariied ofl^. 



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 sagai-tiids was now released and placed in the disii 

 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 fi^agment of Buno- 

 deopsis. 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 wdth 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 other- 

 wise 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- 



