4 Papers from the Marine Biological Laboratory at Tortugas. 



tions. I found a quantitative investigation of this latter point very difficult, 

 owing to the inhibition of normal behavior under artificial conditions, but 

 several experiments showed conclusively that they formed associations. 



METHODS. 



Much care was taken, while observing the behavior of ocypodas and 

 while experimenting with them, to have the conditions as favorable as 

 possible. For the observation of their normal behavior in nature a white 

 tent was used for a time to conceal the observer, but it was found that this 

 was unnecessary and that they could be studied equally as well from the 

 window of a well-ventilated building built out partly over the water some 

 distance from the laboratory proper. From this window, with the aid of a 

 good pair of bird-glasses, many interesting points in the behavior could be 

 distinctly seen without in any way disturbing the crabs. 



The best time of day for watching the ocypodas seemed to be from 

 sun-up until about ii a. m. and from 5 to 6 p. m. During the middle of 

 the day the adults were usually down in their burrows, but there were often 

 a few of the younger ones out at this time. Individuals were also observed 

 during the night, when one might approach quite closely to them without 

 interrupting their feeding. 



A simple trap for collecting ocypodas to be used in experiments was 

 made in the following manner: A deep hole was dug in the sand above the 

 high-tide mark and in it was placed a large dry-goods box without a cover. 

 It was so placed that the open end was flush with the surface of the sand 

 and boards several inches wide were nailed horizontally around the upper 

 edge so as to prevent the crabs from climbing out. On one occasion during 

 the first night 3 individuals were caught ; on the next night the number was 

 increased to 6; on the next to 12, and on the next to 24. While in this 

 special case food and water were kept in the trap, it was found at other 

 times that the trap was equally as effective when nothing of this sort was 

 present. Whether the ocypodas dropped into the trap by accident or whether 

 they were attracted there I am unable to say. 



BURROWS. 



As is well known, Ocypoda lives in burrows which it digs in the sand 

 along the seashore. At Loggerhead Key the large majority of the burrows 

 are found on the sloping beach all around the island, extending from the 

 shore-line to 20 or 30 feet from it, but quite often stray ones occur in 

 the interior of the island many feet from the water's edge. During my stay 

 at Loggerhead Key I found several ocypodas living close to the steps of 

 the laboratory, probably for the purpose of picking up stray pieces of refuse 

 which might be thrown from the doors of the station. Around the kitchen, 

 which is situated over the water's edge, the habitations of the crabs were 



