Habits, Reactions, and Associations in Ocyl'oda arcnaria. 



35 



Several different kinds of labyrinths were used, some of them similar 

 to those employed by Yerkes (1902) and Yerkes and Huggins (1903), but 

 these had to be reversed in the case of Ocypoda, because when the latter is 

 disturbed it always runs away from the water. zMl the observations were 

 made while the observer was jiractically hidden, and healthy active indi- 

 viduals were chosen. 



It was fotmd that labyrinths built of wood and closed up except at the 

 exit w-ere so dark that individuals would hide in them for hours at a time 

 without attempting to escape, and that also labyrinths much more complex 

 than those used by Yerkes and Huggins were of no use, on account of the 

 length of time required for the crabs to find the exit. 



A labyrinth like that used by Yerkes (1902) in his experiments with 

 Carcinus grannlatus was made, but glass plates were substituted throughout 

 for the wood, so as to allow plenty of light to enter. It also had a glass 

 bottom and top and was placed on the beach near the water, properly pro- 

 tected from any disturbance by the movements of people. The glass bot- 

 tom was covered with a layer of sand about 1.5 cm. thick, and a screened 

 pen was built around the exit so that the specimens could not escape entirely. 

 It was found that individuals placed in this labyrinth usually only spent a 

 short time in hunting for the exit ; then they tried to dig a burrow, and fail- 

 ing in this they attempted to escape l)y climbing. Finally they usually 

 settled down and remained quiet, so that they furnished no data bearing on 

 the object of the experiment. 



Finding that individuals nearly al- 

 ways made some attempt to burrow, 

 another kind of labyrinth was devised 

 in which the burrowing instinct might 

 be made use of in escape. While the 

 ocypodas dug their way out in every 

 experiment, they did not usually do 

 so until night. 



Having noticed that nearly all 

 individuals w'ere inclined to climb, 

 when confined, another labyrinth was 

 made in which escape might be ac- 

 complished by this method. A box 

 II inches wide, 15 inches long, and 

 10.25 inches high was divided length- 

 ways into two equal parts by a ver- 

 tical wooden partition {a^ which ex- 

 tended from the top of the box to 

 wuthin 1.5 inches of the floor, thus 

 leaving an opening connecting the two compartments (fig. 10). The 



Fig. 10.- 



-Labyrinth for memory experi- 

 ments. 



