8 Papers from the Marine Biological Laboratory at Tortugas. 



burrow in front of the opening and then very carefully tamp it down, using 

 the broad surface of its large chela and the distal segments of the walking 

 legs. Sometimes, if there is a small hollow in the surface, it will drag sand 

 from another place into the hollow and press it down. Often an ocypoda 

 will carefully tamp the sand that it has thrown away, for a radius of over 

 a foot, and frequently it will smooth off the edges of the opening into the 

 burrow. Almost invariably, unless startled, before an individual goes down 

 into a burrow, either while constructing it or after, it will halt for some little 

 time, apparently surveying the region around to see if there are any in- 

 truders about. 



A most interesting performance that I have frequently observed is the 

 closing of the burrow. This usually occurs after the crab has stocked it with 

 food. Upon several occasions I have thrown a number of small fish to an 

 individual, each one of which was carried down and deposited at the blind 

 end of the tunnel. Then the crab would gather up a load of sand from out- 



2 3 



Fig. 2. Diagrammatic longitudinal section through burrow which an Ocypoda is plug- 

 ging up. 

 Fig. 3. View of plug from above, showing ambulatory appendages tamping surface of 

 plug; mouth reduced to small hole. 



side the burrow, draw it into the entrance, pressing it firmly on one side of 

 the opening (fig. 2). After this it would come out of the half-closed 

 entrance, take up another load of sand, return and enter, drawing the sand 

 after it. This load would be placed alongside of the other and would 

 practically close up the entrance, leaving, however, the distal joints of several 

 of the walking legs outside. With these the ocypoda would carefully tamp 

 down the plug now formed and finally quickly draw them in, leaving some- 

 times only a very small hole and sometimes none at all (fig. 3). By this 

 means the entrance to the burrow was very effectually concealed. 



Sometimes, when individuals are disturbed by other crabs or bv man, they 



