28 Papers from the Marine Biological Laboratory at Tortugas. 



In order to determine if Ocypoda would react to sound-waves the follow- 

 ing experiments were tried : A flute was played upon and large stones were 

 hit together while the observer was hidden 12 feet away, but no movement 

 could be seen that would indicate that the oc3'podas were stimulated. The 

 report of a pistol produced no apparent effect. During a heavy storm the 

 peals of thunder were deafening, but several ocypodas which were along the 

 beach did not return to their burrows nor cease their feeding. These ex- 

 periments and observations indicate that Ocypoda does not hear, but they are 

 by no means conclusive, and a series of such careful experiments as those 

 performed by Fielde and Parker (1904) on ants and Yerkes (1905) on the 

 green frog (Rana clamitans) would well bear repeating before it should be 

 said that Ocypoda does not react to atmospheric sounds. Although it does 

 not seem probable, it might then be found that notes causing a very small 

 number or a very large number of vibrations of the air per second had an 

 effect. 



Ocypoda while eating produces a grinding sound by the movements of 

 its mouth-parts, and at times it also makes a noise resembling the " peep " 

 of young birds, but I have no proof that these sounds stimulate the otocysts 

 of other crabs. 



Prentiss (1901), in his review of the crustacean literature (p. 228), 

 has cited two well-known examples of noises, the one a case of stridulation in 

 PaUnurus vulgaris,'^ described first by Mobius (1867) and later (more cor- 

 rectly probably) by T. J. Parker (1878), and the other the pistol-like report 

 of Alpheus described by Goode (1878). To these may be added the stridu- 

 lation of Ocypoda, although I have never 

 been fortunate enough to hear it. Often at 

 night I have stayed on the beach among the 

 feeding ocypodas in the hope of hearing the 

 stridulation, and I have listened at the en- 

 trance of the burrows which were occupied 

 by individuals. I have good reason, how- 

 ever, to believe that the stridulating noise is 

 made, since I have often seen ocypodas go 

 through the motions that would produce it 

 when they were attempting to gain possession 

 of a burrow occupied by another specimen. 



Along the inner surface of the palm of the cheliped in the individuals 

 there is a row of fine tubercles (stridulating ridge, plate 3), which when 

 the cheliped is bent, as shown in text-fig. 8, comes in contact with a process 

 on the basal joint. By moving the distal part of the appendage from side 

 to side the row of tubercles is rubbed against the process and a sound is 

 produced. I have seen this movement frequently in the case of individuals 



Fig. 8. 



-Position of chela during 

 stridulation. 



' Metitioned first by Leach in Malacostraca Podophthalmata Britannise, 1815. 



