STUDY ON THE HABITS OF THE CRAB. 175 



2. If the crab has carried an artificial plastelin case on its back 

 for a long time, it often happens that it chooses its own plastelin 

 case, even if near to it there is a sponge of suitable size. 



3. Dromia may be found without any case at all. Such an 

 animal always chooses a sponge, and so does an individual which 

 remained in the aquarium uncovered for a certain time. 



4. We give cases of different kinds to an individual, which 

 carries its own case on the back. If the latter was a paper case, 

 then Dromia always drops it and chooses a sponge. Under the 

 same conditions a case of plasteline was dropped only sometimes, 

 but a normal case of sponge was nearly always kept by the 

 animal. 



CONCLUSIONS. 



To a certain extent the described facts furnish an answer to 

 the questions raised at the beginning of this paper. It follows 

 certainly from them that there is no reason to speak about 

 symbiosis of Dromia and sponge, as the mutual adaptation is 

 entirely lacking. If the crab is especially adapted to carry a 

 case on its back, the sponge surely remains completely passive. 

 The lack of any specificity of the symbiosis proves it very clearly. 

 It is not plain what may be the use of the sponge to Dromia. 

 Polimanti put covered and uncovered Dromia into an aquarium 

 containing an Octopus. He found that the uncovered individuals 

 were devoured, just as any crabs of some other species, but the 

 covered ones remained safe. However Polimanti does not 

 decide whether the Octopus simply was unable to see the covered 

 animals, or whether the sponge held it away. At all events, as 

 far as the optical side of the problem is concerned, it may be 

 interpreted in different ways. In most cases there is no corre- 

 spondence in color between the sponge and the surroundings. 

 The sponge, which Dromia carries on it, may be of very different, 

 often bright, colors : red, yellow, purple, etc. The presence of the 

 sponge even facilitates the catching of Dromia, as the crab usually 

 remains on vertical walls very near to the surface of the sea. 

 An uncovered specimen is less conspicuous by far, on account of 

 its uniform gray or brownish coloration. But just as frequently 

 the sponge may be of a somewhat protective coloration, gray, 

 brownish, or greenish, which contradicts again the theory of a 



