898 COMMENT LlSitt BENEFICIAL TO CRUSTACEA, 



gastropod shell, while the rest of its body lies in a spiral canal 

 continuous with that of the shell and gradually prolonged from 

 it with the growth of the two associated organisms. The small 

 shell was evidently inhabited by the young crab when the asso- 

 ciation began, but had become deeply buried in the sponge at the 

 time when the experiments were made. The sponge was of the 

 usual orange-red colour, although they are sometimes dark and 

 comparatively inconspicuous. In size and shape it resembled a 

 smallish potato. 



When disturbed or frightened in any way, the crab darted 

 back into its sponge exactly as other Hermits dash into their 

 shells. 



In order to obtain pictures of this species and P. hernhardus 

 under as na,tural conditions as possible, the objects dredged up 

 with each species were ari-anged in a dish, which was lowered into 

 an aquarium so that its edge was in contact with the glass front 

 and its contents well lighted from above. The cr.abs were 

 secured in the most convenient position by tying to a stone in 

 the dish. Although the string was wound so as not to touch 

 F. cuanensis, and was, in fact, separated from its body by a con- 

 siderable thickness of sponge, the crab quite understood the 

 situation, .and spent the whole time the artist was at work in 

 trying to wear through the string with its two large claws. 

 Thus occupied and stretching out of its canal, it was an 

 admirable sitter. 



Prof. Grarstang had already recorded that sponges as a group 

 are intensely disliked by fishes *, but I was anxious to test this 

 special example and compare its palatability with that of the crab. 

 Pieces like those of the Sagartia were therefore thrown into the 

 aquarium, but were I'ecognized as unpalatable even more quickly 

 than the others, and seized by fewer fishes. "When taken they 

 were instantly rejected. The Fagtirus was then ofiered deprived 

 of his sponge ; there Avas a wild sti'uggle, and the fortunate 

 captor swallowed him in a moment. 



It was evident that both these Hermit-crabs are associated with 

 organisms possessing qualities rendering them unpleasant to fishes 

 —qualities advertised by conspicuous wai-ning colours. One of 

 the crabs was shown on this occasion to be very palatable to fishes, 

 and the other previously by Prof. Garstang, to be much sought 

 after by them. Although the experiments described were very 

 few, the results were so definite and clear that there can be little 

 doubt about the meaning of the association in these and other 

 similar examples of commensalism in Crustacea. 



The beautiful illustrations, projected upon the screen, were 

 painted in 1890 by my friend the late Mr. H. M. J. Underbill, of 

 Oxford, who has reproduced the appearance of the living animals 

 in their natural surroundings with wonderful skill. 



* " C!olom's of Animals," 1. c. 



