Habits, Reactions, and Associations in Ocypoda arcnaria. 29 



that seemed to be excited, and it was performed with great rapidity. There 

 is scarcely any doubt that the sound is produced, but I have no reason to 

 beUeve that other ocypodas hear it. However, the vibrations produced by 

 the rubbing might easily be transmitted to the sand and thence to the sensi- 

 tive tactile hairs on the ambulatory appendages of another individual, thus 

 producing a tactile stimulus. 



In Mier's (1876) paper it is stated that in one species of Ocypoda the 

 stridulating ridge is absent in the very young individuals. I have examined 

 many specimens of 0. arcnaria, the smallest i cm. across the carapace, but 

 have always found the ridge present. It is of interest to note that the land- 

 crab, Gecarcinus, which is found in abundance on Loggerhead Key and 

 which lives under very similar conditions, has no stridulating ridge. 



As has been pointed out by Prentiss (1901), it does not follow that an 

 animal is able to hear because it makes a noise, and as yet we have no ob- 

 servation or experiments proving that Ocypoda or any other crustacean has 

 audition. 



Many attempts were made to repeat the experiments performed by Beer 

 (1898) and Prentiss (1901), in which the behavior was observed after the 

 removal of one or both of the otocysts. In every case in which both of these 

 organs were removed the individuals did not live long enough to recover 

 from the shock. As a general rule, even the removal of one otocyst caused 

 such profuse bleeding that the specimen soon died. The behavior of oper- 

 ated individuals, however, was very similar to that observed by Prentiss 

 (1901). Those ocypodas which had their eyes painted, so that there was no 

 reaction to sudden changes in the intensity of light, retained their equilibrium 

 as well as normal individuals. The only difference in behavior was their 

 tendency to remain quiet. While the eyes undoubtedly assist in maintaining 

 the equilibrium, they are not the most important organs in this respect. 



The removal of one otocyst brought about some disturbance in equi- 

 librium, part of which may have been due to the shock, but the removal of 

 both otocysts caused very marked eflfects ; individuals when placed on the 

 sand usually turned one or more somersaults. While these disturbances 

 may have been partly due to the operation, tlicy were undonbtedlv largely 

 the effect of the loss of organs that regulate the equilibrium. 



TACTILE SENSE. 



While Ocypoda probably does not hear, the tactile sense is well devel- 

 oped and is a very important factor in regulating this animal's activities. 



As would be expected, Ocypoda is quite sensitive to jars transmitted to 

 the sand. I have often watched individuals which were part way down in 

 their burrows, but not so far that the legs of one side might not be seen. 

 Under these conditions, a movement of my foot in the sand or a step within 

 3 or 4 feet caused the specimen to react by a sudden movement, even when 



