Habits, Reactions, and Associations in Ocypoda arcnaria. 5 



very numerous, and at certain times of the day large numbers could be seen 

 moving around near it in search of food. 



Ocypoda usually makes its burrows on the sloping beach ; in some cases, 

 however, they occur on perfectly level ground, and in others, where the 

 beach has been washed away, they are found dug into the vertical surface of 

 the shore. There are three kinds of burrows, all very simple. One consists 

 of a tunnel which is not perfectly straight, extending down into the sand at 

 an angle of about 45° with the surface. This tunnel opens to the exterior 

 at one end, terminates blindly at the other, and has a more or less vertical 

 passage branching off from it and sometimes communicating with the ex- 

 terior by an opening (see fig. i). The opening of the vertical passage is 



-T'"" 



Fig. I. — Longitudinal vertical section throvigh a burrow with two openings. 

 a, entrance; A, opening for escape. 



always farther away from the water-line than the main tunnel. As a rule 

 these burrows extend directly away from the shore-line, but sometimes they 

 do not exactly. The depth varies considerably, averaging i or 2 feet. An- 

 other kind of burrow, which occurs higher up on the beach, is like those 

 just mentioned except that it is much deeper and does not have any branch- 

 ing passage. One of these, when carefully followed to its end, was found 

 to extend 4 feet 2.5 inches, ending in coarse, wet sand. It occurred to me 

 that these deep burrows might be used by the females during the breeding 

 season and also that they might be used for molting purposes, but I have 

 no observations to support the truth of these statements. As a matter of fact 

 I have never found females with eggs at the bottom of their burrows, nor 

 have I found casts. It is also true, however, that I have never found the 

 casts on the surface of the ground. 



Very young ocypodas make still another kind of burrow which extends 

 vertically downward into the wet sand for only a few inches. 



The burrow first described is much more numerous than any other kind 

 and is more interesting on account of the branching passagewa}' connected 

 with it. I have examined many of these burrows in the effort to find the 

 use of the branch. As stated above, sometimes the passage opens to the 



