J 68 \V. S. DEMBOWSKA. 



it begins to work systematically, tearing off small pieces of sponge 

 along a fairly regular elliptical line, while it turns slowly at the 

 spot. A regular elliptical furrow results, which goes through the 

 whole thickness of the sponge reaching down td the surface of 

 the stone. This furrow is the outline of the future case. Xow 

 Dromia grasps the periphery of the furrow at two points and 

 pulls it towards itself trying to tear the sponge off. This move- 

 ment differs very distinctly from the behavior of Dromia while 

 cutting the sponge through. As the sponge holds very tightly 

 this attempt usually remains without success. Following this 

 Dromia begins again to tear pieces of sponge, but now it works 

 along the furrow trying to press the chelae between the sponge and 

 the stone. Sometimes the animal proceeds in one direction 

 towards the center of the sponge, remaining at the same spot 

 during the work, but often it detaches the edge of the sponge 

 from the stone along the whole circumference of the furrow. 

 In the former case it starts the work from below, sitting on the 

 future case and directing its head downward. All the time the 

 planes of both chelae remain parallel to the surface of the stone 

 and the work now is much more a systematical detaching than 

 cutting, as only few pieces of the sponge are now torn off. After 

 some time the crab tries again to tear off the whole case, grasping 

 the edge of it at two points and pulling it towards itself. Usually 

 this second attempt is made at the right time and the animal, 

 holding the sponge tightly, rolls with it from the stone to the 

 bottom of the aquarium. If however, the attempt was pre- 

 mature Dromia returns at once to the interrupted work and 

 after some time repeats the same attempt once more. Sooner 

 or later there always results a case corresponding very exactly to 

 the size of the animal. 



It seems that a suitable consistency of the sponge, rather than 

 the curvature of the stone corresponding to the curvature of the 

 animal's back, decides the choice of the spot where Dromia 

 starts its work. Therefore very often the manufactured case 

 is too flat and it does not fit exactly to the surface of the back. 

 The crab corrects this by pressing the sponge tightly to the back 

 and bending it out. As the tissues of the sponge are fairly 

 plastic, the resulting curvature of the sponge becomes somewhat 



