Habits, Reactions, and Associations in Ocypoda arcnaria. 13 



not react. There was no movement of the antcnnje, svtch as Bethe (1895, 

 1897) has observed when a piece of meat is held near the mouth-parts, but 

 when the fish was touched against one of the chelre the ocypoda immediately 

 jumped at it, took hold, pinched it, and put its chela up against its mouth- 

 parts, after which it began to eat. There is nothing in the behavior of the 

 crab in this experiment which proves that Ocypoda reacts to odors. How- 

 ever, the rapidity with which it determined that the object was food after 

 the chela was touched leads me to believe that it had been stimulated by the 

 odor of the fish before the chela was touched and that it inhibited the reac- 

 tion on account of the abnormal conditions to which it was subjected. It 

 is true that the fleshy consistenc}- of the fish may have been a food- 

 determining factor. 



•'•.'•."•■■•.■•.•.■•r:iWi ^■.■.-•y.'':":'"/''^.'. .'■^'■\i-:.::'!yr\--:-''vV^^}^'^.y-- . 



•*^5=?^i>!; ;.■;.' 



Figures illustrating experiment 5. Fig. 4, ver- 

 tical section ; fig. 5, seen from above. 



In the following experiments an attempt was made to find out from how 

 great a distance Ocypoda would react to food. A square 9.5 inches by 9.5 

 inches, divided up into 64 smaller and equal squares, was marked out on the 

 sloping beach in a region where it could be seen by the experimenter while 

 he was practically concealed about 10 feet above the sand in a house nearby. 

 Small pieces of decomposing fish about 1.5 c.cm. in volume, fragments of 

 coral, and pieces of black glass were used to attract the crabs. 



Experiment A. — A piece of fish was placed at the center of the square, 

 as shown in fig. 6. An ocypoda came to point A^ and began to make a 

 burrow. After a few digs it went straight for the center of the square {A„) 

 and grabbed the fish with no hesitation. The wind was blowing in the direc- 

 tion shown' and the meat was on the surface of the ground. An important 

 condition in this experiment, as we shall see in another section, was that flies 

 were moving about on the meat and frequently flying to and away from it. 



Experiment B. — The conditions in this experiment were the same as 

 in Experiment A and the results were the same except that the crab stopped 

 at Br, for 2 or 3 seconds while on its way to the meat. 



While the crab in these two experiments may have reacted to the odor of 

 the fish, the eyes undoubtedly received a stimulus that determined the move- 

 ment toward the food. 



Experiment C. — A piece of fish meat was placed in the center of the 

 square. A crab 2.5 feet from the center (Cj) went directly to the meat 



In experiments A to J the wind was blowing across the square from the upper 

 left-hand corner to the lower right-hand corner. 



