Ij6 W. S. DEMBOWSKA. 



warning color. It will be safer probably to conclude that the 

 color of the sponge is an accidental one and that it does not 

 serve any special purpose. 



The conformity of the inner surface of the sponge and of the 

 back of Dromia, especially in young individuals, may be explained 

 without any artificial assumptions, like the theories of Renier 

 and Yosmaer. We did see that the animal possesses the faculty 

 of cutting a sponge of suitable size and circumference, tearing it 

 off from a stone, and putting it on its back. As the sponge re- 

 mains then pressed tightly to the back of the crab, it soon assumes 

 a suitable shape. When moulting the crab must drop the sponge. 

 But we know that all the crabs after the moult remain nearly 

 motionless until the new chitin hardens. We know moreover, 

 that Dromia can find a sponge which is entirely covered by stones, 

 and that it can dig it out . It follows therefrom, that very often 

 at least after the moult the crab may pick up its own sponge 

 again. But still we do not know exactly if the rapidity of growth 

 is the same in both organisms. At all events it must happen 

 very often that under its natural life conditions Dromia is com- 

 pelled to find a new case for itself. 



The described facts confirm once more the very complex 

 character of reactions of a crab. The behavior of the animal 

 towards the case is a series of most complicated movements, too 

 complicated in fact to be explained by simple external stimu- 

 lations. From the physiological point of view there exists the 

 possibility that the pressure of the case on the sensory hairs of 

 the animal's back and the effect of its weight on the 4th~5th 

 pairs of ambulatory legs form the stimulus which inhibits the 

 movements leading to the finding and manufacturing a new 

 case. Conversely, the lack of such stimulus may be one of the 

 causes of those movements. But there exists an interesting 

 fact that contradicts the above assumption. One individual, 

 while carrying on its back its normal sponge case, began to manu- 

 facture a new case from a piece of paper, without dropping its 

 sponge. Such facts are rare, it is true. However, it happens 

 more frequently that individuals, which are carrying a case of 

 plasteline or paper, choose a sponge and grasp it with the chelae, 

 and only now drop their cases from the back. This behavior 



