NOTES OX THE BEHAVIOR OF THE FIDIH I k CRAB. \'t~ 



the interpretation is very difficult. As mentioned above a quick 

 pouring of water in the jar causes the walls to collapse, thus 

 destroying the burrow completely. The animal forces itself 

 through the sand and after the water has been removed it digs a 

 new burrow in quite a new spot. But if the burrow was tightly 

 closed Uca begins to work methodically, provided that the 

 "tide" has gone out. Its movements are now somewhat the 

 reverse of the ordinary burrowing. It will be remembered that 

 the animal while remaining motionless in the air-chamber has 

 its large chela directed to the inside. Now the outer legs, 2, 3, 4. 

 grasp a sand pellet from the roof of the chamber and push it 

 down towards the sagittal axis of the body. Then the crab 

 climbs a little upward until the pellet lies between the carapace 

 and the legs II., III., IV., which grasp it in turn. Uca comes 

 down again and the sand will be deposited and kneaded at the 

 bottom of the chamber. Still pursuing this work, the animal 

 causes the chamber to rise slowly in an oblique direction, still 

 keeping its volume unaltered, as the sand is always only carried 

 from the roof of it to the bottom. At last the fiddler emerges, 

 leaving the former canal filled with sand behind itself. Only 

 the upper part of the burrow corresponding to the chamber in 

 the last moment of work remains open. Now the crab may 

 roam for a long time around the jar or it will start digging a 

 new burrow at once. In most cases it works now along the 

 same way, entering the hole from which it has emerged and 

 following the same track. Usually it carries then the removed 

 sand out of the burrow and the whole canal remains open. 

 But, curiously enough, often will the crab close the canal behind 

 it. After some time Uca is sitting again in the air-chamber at 

 the bottom of the jar, while the whole burrow is tightly filled 

 with sand, as if the animal wanted only to breathe fresh air for 

 a while. In following the previous track the crab is evidently 

 guided by the smaller resistance of the sand filling the burrow 

 as compared with the surrounding. If the jar was filled with 

 water for some time the sand collapses and there is no difference 

 in its consistency. In this case Uca digs itself out once more, 

 but does not follow exactly the previous track and sometimes it 

 will dig in a perfectly vertical direction. In the apparatus 



