174 ^'. S. DEMBOWSKA. 



It then climbed over the sponge, very soon found the wire hook, 

 and began to tear off small pieces of sponge around it. After a 

 short time the sponge became liberated and the Dromia rolled 

 down with it, and put the sponge on the back. From the moment 

 of putting the crab into the vessel to the liberation of the sponge 

 7 minutes elapsed. I repeated this experiment several times and 

 I found that the described behavior is a typical one. Shortly 

 after liberating the sponge I took it off again, giving to the 

 animal the paper case which was accepted. Then the sponge 

 was again attached very tightly to a wire hook and was hung on 

 the wall. After being put into the vessel, the crab once more 

 directed itself immediately towards the sponge, climbed over it 

 and only now dropped the paper case. The next moment it 

 adjusted itself in the sponge, grasping its inner surface with the 

 4th~5th pairs of legs and pressing the back to the concavity of 

 the case, assuming its normal position. Now the animal tried 

 to go with the sponge, but naturally succeeded only in gliding with 

 the legs on the smooth wall of the vessel. Then it changed 

 several times its position in the sponge, still holding it tightly, 

 but only after two hours of continuous attempts it found the 

 wire hook, with the chelae. Now the liberation took only few 

 minutes and as before Dromia rolled with the sponge to the 

 bottom. I repeated this experiment with the same individual 

 over 60 times in about 20 days and found that in the great 

 majority of cases the animal directs itself immediately to the 

 wire hook and only very rarely, and during a short time, it 

 tries to go with the sponge on the back. The time of liberating 

 varied from 6 to 20 minutes, on the average it was 8 minutes. 

 Many other individuals showed exactly the same reactions. 

 After some time, ordinarily after a few minutes, each crab 

 succeeded in finding the wire hook and liberating the sponge. 



It is to be noticed that Dromia possesses a marked faculty of 

 choosing the material for its case, which depends somewhat on the 

 past of the animal. Several facts corroborate this conclusion. 



i. We take off the sponge from a fresh Dromia and we put 

 into the aquarium several different materials, such as a sponge, an 

 artificial case made of plastelin, a piece of rag, paper, etc. Under 

 those conditions, the animal chooses the sponge. In most cases it 

 recognizes its own case from many other sponges. 



