36 Papers from the Marine Biological Laboratory at Tortugas. 



ocypodas experimented with were introduced into the posterior compart- 

 ment, shown in fig. 10, through the sHding door indicated (b'). The front 

 of the box (c), instead of being of wood, was made of ordinary fly- 

 screen. At {d) and ie) on the floor of the box were placed two pieces of 

 wood 2.4 inches long and 1.6 inches high, which divided the anterior com- 

 partment into three passageways. In the top of the box at (/), {g) and 

 (/r) were set three windows 2.6 inches by 4 inches, made of ordinary 

 window-glass. In the center of the middle window {g) an opening was left 

 which was the exit from the labyrinth, and around this window was erected 

 a barrier {i) which prevented the crabs from climbing out over the box. 

 Similar ones (j) {k) were placed around the other windows so as to make 

 the lighting the same in each case. In escaping a crab would have to pass 

 from the posterior compartment into the anterior compartment, climb up 

 the screen, pass through the opening in the middle window, and then climb 

 down tlie outside of the screen to the surface of the sand in the pen. This 

 pen was inclosed by panes of window-glass, 10 by 15 inches, set vertically. 



Six active ocypodas were used in the following tests, but one of these 

 soon died and another was lost, so that in the table below only the time 

 records of four individuals. A, B, C and D, are recorded. As a rule each 

 crab was given two trials a day, and precautions were taken to guard the 

 individuals from disturbing influences of moving objects. 



In general there seems to be a decrease in the time required for escape 

 up to the eighth day, but after that the average time increases. This increase 

 may have been due to the condition of the crabs. During the climbing 

 after the eighth day they fell frequently, and this undoubtedly had a bad 

 effect on them. 



Time required for escape from labyrinth, recorded in minutes. 



During the first few experiments the behavior was as follows : Indi- 

 viduals when introduced into the posterior compartment almost invariably 

 ran to the left side; then if active they went into the left passageway and 

 up the screen, usually following the corner of the box quite closely; on 

 arriving at the top they would scratch the left glass window, apparently 



