Habits, Reactions, and Associations in Ocypoda arcnaria. 37 



attempting to get out, but failing in this they would either crawl along the 

 edge of the window toward the right until they reached the opening in the 

 middle of the center window, where they would climb out and down into 

 the pen, or they would descend again into the box and after a time repeat 

 the climbing either in the left-hand or right-hand side and occasionally in 

 the middle part of the screen. 



Although the time records do not indicate that the ocypodas learned the 

 position of the exit, yet the behavior, after about 5 days, began to indicate 

 that all the individuals had learned it more or less perfectly. They still 

 continued to crawl up along the corners of the box, but they now often 

 climbed across the screen in a diagonal direction toward the exit, from 

 either the right or left passage-way. Toward the end of the series of tests, 

 the ocypodas became quite inactive, often refusing for a long time to move, 

 but when they did become active they frequently climbed almost directly 

 toward the exit. 



The fact that in the above labyrinth experiments we do not obtain good 

 quantitative evidence of memory does not show that Ocypoda is without 

 memorv. It must be admitted that the labyrinth used was a rather difficult 

 one and that the tests did not extend over as long a period as they should. 

 The injury experienced by frequent falls from the screen and the somewhat 

 artificial conditions undoubtedly affected the results. 



Another experiment performed shows that Ocypoda profits by experi- 

 ence. It had been noticed that individuals in the trap made use of the sea- 

 water given to them in glass dishes in much the same way as individuals 

 under natural conditions use the water in the sea. Accordingly a trap was 

 thoroughly cleaned and stocked with several ocypodas caught in another 

 part of the island. A study of the behavior was then made when a dish 

 of sea-water was put in th trap. Care was taken not to allow any of the 

 water to drop on the sand and the dish was buried until its rim was level 

 with the surface of the sand. The ocypodas apparently did not pay any 

 attention to the dish at first, but after a time, seemingly by chance, they 

 crawled until their legs projected over the edge and into the water. Usually 

 when this occurred to an individual it would settle down, digging the legs 

 of the other side into the sand as it does when waiting for a wave. After a 

 time it often climbed over into the water and moistened its gills. This ex- 

 periment was repeated for several days, a dish of water being given to them 

 twice a day, and many of the crabs soon went through the same behavior 

 almost as soon as the water was introduced. Finally a dish without water 

 was tried and it was found that some of the crabs behaved in the same 

 manner as when water was in the dish, i. c. they crawled up to its edge, 

 settled as though waiting for a wave, and then finally climbed over into the 

 dry dish. 



This behavior I interpret as a case of associative memory, in which the 



