196 JAX B. DEMBOWSKI. 



The lowest interval is 308, the highest 434, which corresponds 

 or a difference of 2 hours 6 minutes. As such an irregularity 

 tuns all the year round it would be a pure wonder if the "memory" 

 would compel an animal living under constant conditions to 

 accomplish its tasks at the same intervals. I do not intend to 

 discuss the rich literature on periodicity of organic functions, 

 but I have a strong impression that the whole question has a 

 lot of metaphysics in it. 



In fact I never noticed any intrinsic periodicky in my crabs. 

 When put into the jar the crab digs the burrow, closes it and 

 remains in the air-chamber for a very various time. Sometimes 

 it will dig itself out in a few hours, sometimes it remains quiet 

 for 3-4 days. If we put water into the jar while the chamber is 

 tightly closed the crab does not go out even for a week. If we 

 suck all water out Uca usually digs itself out in 3-4 hours, but 

 sometimes it does not stir for many days. Its behavior must be 

 ascribed to actual external factors, not to the remembered ones, 

 although we are very far from understanding which factors are 

 working. When the sand begins to dry Uca closes the burrow. 

 It does the same when we pour slowly water into the jar and the 

 sand becomes wet. From a certain point of view such reactions 

 may be called memory, since the crab does the same as it has 

 done under its natural conditions. We imitate those conditions 

 as closely as possible and sometimes we get the same reaction. 

 It is also not true that the fiddler closes its burrow "before the 

 tide." It does it always during the tide, when the sfcwly rising 

 water has moistened the air-chamber, not yet covering the 

 surface of the ground. The arising slight movement of sand 

 grains or the walls of the chamber becoming softer may be 

 perceived by the crab as the beginning of the tide. As far as I 

 observed Uca never remains a long time on the surface of the 

 ground without visiting from time to time its burrow. 



And thus, exactly as in heredity, not .1 ui\rn reaction in itself 

 characterizes an animal, but always the faculty of producing 

 this reaction under given conditions. 



5. What becomes of the burrow after the tide? The tide 

 destroys a part of the burrow and the era!) must dig itself out. 

 This may be done in several manners and I must confess that 



