1 66 



W. S. DEMBOWSKA. 



all this the crab retains a firm grasp on the paper. Nearly 

 always Droniia works at the middle of one edge of the square, 

 much more rarely the animal cuts off one of its angles. But it 

 is only extremely seldom that the new paper case lies unsym- 

 metrically. It seems probable that the equilibrium plays an 

 important role therein. 



During two months each of my crabs has been observed several 

 times while working at its new case. There is some evidence that 

 every individual has its own system of working. Four typical 

 modes of cutting may be distinguished. The case is manu- 

 factured: 



A. In the middle of the longer side of the rectangle. 



B. In the middle of the shorter side of the rectangle. 



C. At the corner. 



D. Somewhere unsymmetrically. 



Those four positions are to be seen in Fig. I. In Table I. I have 



B 



D 



FIG. i. The four modes of cutting a paper-case. 



put together how many times every individual cut the case in 

 each of the above four positions. Only few crabs, as Nos. VI I. 

 and IX., did not show any regularity of w r orking. The re- 

 maining ' individuals showed a marked predominance of one 

 mode, especially if we take into consideration that the modes 

 A and B are very similar. 



