14 Papers from the Marine Biological Laboratory at Tortiigas. 



-C, .Ct 



2 ''i FCr rOM CN TER . 



(Cj), returned to C^ and went down into its burrow. A brisk wind was 

 blowing directly away from the crab and there is no doubt that the latter 

 did not react to the odor of the fish. 



Experiment D. In this experiment a piece of black glass 2 cm. wide and 



4 cm. long was stuck in the 

 sand at the center of the 

 square. A crab at Dj, fac- 

 ing away from the center of 

 the square, moved slowly 

 but straight for the black- 

 glass. To my surprise it 

 went backward all the way, 

 striking the glass squarely 

 in the middle of the pos- 

 terior side of the carapace. 

 Later it was found that 

 this was not an unusual 

 way for a crab to approach 

 an object. After digging 

 around the piece of glass 

 and pinching it several 

 times it was abandoned. 

 Here odor could not have 

 been a factor in the beha- 

 vior of the crab nor could 

 the movement of flies, for 

 there were none present. 

 Experiment E. A piece of white coral about 2 by 4 cm. was placed at 

 the center of the square. A crab whose burrow was at ; came out, but 

 showed very little inclination to examine the coral. It was almost 5 minutes 

 before it started for the coral and then it moved slowly. As in the case 

 of experiment D, flies were not present. 



Experiment F. Several pieces of white coral smeared with the juices of 

 decomposing fish were placed at the center of the square. The subject of 

 the experiment in experiment E did not move toward the coral at once, but 

 as flies began to alight the crab approached and attempted to get something 

 to eat off of it. Soon, however, it returned to its burrow. The flies which 

 had been driven off by the attack of the crab then came back and with their 

 return the crab quickly approached the center of the square. Instead of 

 leisurely taking hold and pinching the coral it gave a little jump in the 

 seizure, as it does in the case of a live fish. The flies were driven away, 

 after which the ocypoda returned to its burrow. This performance was 

 repeated fifteen or twenty times, approaching, jumping, seizing and return- 

 ing, after which the coral was abandoned, the crab apparently paying no 

 more attention (objectively speaking) to it nor to the flies collected upon it. 

 The ocypoda then began to dig its burrow, and when other individuals came 

 and attempted to eat from the coral it did not chase them away, but merely 

 stood guard at the entrance to its home. 



The eyes in this experiment played the most important part in the 

 behavior of the crab, and there is no doubt that Ocypoda associates the pres- 

 ence of flies, or rather the difTerence in the intensity of light resulting from 

 the movement of the flies, with the presence of food. Its behavior can 



Fig. 6 Diagram of paths taken by 

 ocypodas in experiments A to F. 



