NOTES ON THE BEHAVIOR OK THE K11JD1.ER < k\H. 



burrow becomes bent and it approaches continually to the 

 horizontal plane. This tendency explains to a certain extent 

 why the burrow is never straight. The animal must hide itself 

 in the sand and the shortest way of doing it would be the digging 

 in a vertical direction. On the other hand the burrow must 

 approach the horizontal line. Both tendencies working together 

 cause the burrow to become bent. From a mechanical point of 

 view we might expect that the crab will dig in the direction of 

 a diagonal. Thus the burrow forming a curve shows that the 

 causes are more numerous and a mechanical explanation is far 

 too simple. 



The biological significance of the end-chamber and of the 

 burrow being bent follows from a simple experiment. When 

 the animal has finished its work and it is sitting motionless in 

 the end-chamber w r e begin to drop slowly sea water into the jar. 

 Very soon the water reaches the crab. The animal begins to stir, 

 then it climbs up to the mouth of the burrow and closes it. 

 To do this Uca, usually sitting in the burrow with its large 

 chela directed towards the entrance, goes entirely out, turns 

 and enters the burrow with the chela I. forward. When the 

 body is so deep that the bent legs 2-5 touch the edge of the hole 

 they grasp this edge and pull it strongly inward. This time the 

 legs are held close together and the leg 5 participates in the 

 work like the others. There results a pellet of sand which is 

 dragged down and adjusted carefully to the side wall of the 

 canal close to its entrance. The pellet is followed by the second, 

 third, etc., until a solid cork is formed closing tightly the hole. 

 On the surface of the sand at the spot where the hole was, 

 there remain radial furrows converging towards the former center 

 of the hole. This process was already described by Pearse and 

 others. But the task is not yet finished. Uca grasps the sand 

 inside the burrow and carries it to the top, adjusting the pellet 

 to the new formed roof of the hole. Very many pellets may be 

 handled in the same way and a thick cork arises which closes the 

 burrow tightly. We may pour so much water as to cover the 

 sand completely. If at the beginning we dropped the water in 

 very slowly the animal had enough time to close the burrow 

 carefully. In this case, and such is the case under natural 



