PRENTISS : THE OTOCYST OF DECAPOD CRUSTACEA. 227 



place only when the animal was within a few centimeti'es of the vibrat- 

 in<^ surface, and was most marked wlien the antennae and antennules 

 were in close proximity to it. After blinding the animals and removing 

 their otocysts, no apparent difi'erence could be detected in the reactions 

 called forth, as compared with those of normal crabs ; removal of the 

 first two pairs of appendages caused, on the contrary, the responses to 

 almost completely disappear. 



b. To Atmospheric Sounds. As the fiddler crab is on land a large 

 part of the time, a number of experiments were tried to determine the 

 effect of aerial vibrations upon them when they were feeding under per- 

 fectly normal conditions. A position for observation was selected near 

 a bank which was completely honeycombed by their burrows, where 

 one could see the animals perfectly well, and yet be screened from their 

 view by intervening bushes. If one remained perfectly motionless, the 

 animals would come within a short distance of the observer's place of 

 concealment, feeding as unconcernedly as if no one were near. When a 

 number of crabs were little more than five feet distant, a horn was blown, 

 care being taken to direct it away from them. Although a sound was 

 thus produced loud enough to be heard at some distance, all the animals 

 continued to feed undisturbed. 



The striking together of two stones, and the sound produced by str-ik- 

 ing an iron pipe with a stone (the objects in both cases being held in 

 the hand) also had no effect upon them. On striking the ground with 

 a heavy stone all the crabs within a radius of ten or twelve feet were 

 startled ; some of them merely stopped feeding, while others scuttled 

 into their burrows. The same result was brought about by simply 

 stamping upon the ground. If a quick movement was made in the 

 sight of the animals, they at once scattered precipitately to their holes. 

 These observations were repeated a number of times, and on crabs of 

 two different localities, with the same results. 



From these experiments and observations, we may draw the conclusion 

 that the fiddler crab, whether in water or on land, does not respond to 

 true sound-stimuli, but is affected only by jars or vibrations transmitted 

 to the water or to the ground. In neither case can they be said to hear. 

 When feeding upon laud they do not depend upon an auditory sense to 

 protect them from terrestrial enemies, but rely entirely upon their keen 

 vision and delicate tactile organs. 



The statement is generally accepted, that all animals which produce 

 sounds also have a sense of hearing, and this is advanced as an argu- 

 ment in favor of audition in Crustacea. The two well-known examples 



