STUDY ON THE HABITS OF THE CRAB. 173 



attempts will be unsuccessful now, the animal presses its fore or 

 hind end between the sponge and the ground until it overthrows 

 the case and causes the stones to fall out. We have seen already 

 that the crab behaves sometimes in that way when the sponge 

 lies with its concavity downward. It will be noted, however, 

 that the animal never does this when the sponge points with its 

 concavity upward and there is no doubt that this behavior is 

 caused by the impossibility of using one of the ordinary ways. 



In other cases the stones will be pushed with one chela towards 

 the edge of the sponge until they fall out. This work is but 

 seldom carried to an end and some of the stones usually remain 

 when the animal puts the sponge on its back. The remaining 

 stones prevent the proper adjustment of the sponge and after 

 some time Dromia repeatedly lifts the sponge over its back and 

 presses it again, which finally causes the stones to fall out, slipping 

 between the back of the animal and the inner surface of the 

 sponge. 



Dromia can manage the liberating even in cases when the 

 sponge remains completely covered by the stones and invisible. 

 This requires however some previous learning. Every time that 

 the crab succeeds in putting the sponge on the back, we take it 

 off and put still more and more stones into it, keeping the sponge 

 always at the same point of the bottom. After some time 

 Dromia becomes accustomed to the place where the sponge lies 

 and it goes directly towards it, trying to move the stones and 

 liberate the sponge. This behavior becomes striking when, after 

 several repetitions, we put the sponge in quite a different place. 

 The animal goes nevertheless directly to the previous spot and 

 begins to seek the sponge. As control experiments showed, it 

 never behaves in this way without previous learning. 



In another series of experiments I fastened the sponge to a 

 little wire hook. In the meantime the crab manufactured a new 

 case of paper. In order to make the sponge more conspicuous I 

 chose a red one and put it into a porcelain dish, hanging it so 

 high on the wall that the crab could hardly reach it. When I 

 put the crab in, it directed itself at once towards the sponge, 

 dropping the paper case on the way. With some difficulty the 

 animal succeeded in grasping the hanging sponge with the chelae. 



