Tone perception in gammarus pulex

The proof of the existence of a restricted tonal sense in any animal would be of great interest. The present paper offers evidence of the occurrence of this phenomenon in the Gammarids. Though it must be admitted that the number of animals which responded to the tests was small, the response, when it occurred, was so definite and unmistakable that a description of the; results seems desirable. My attention was first directed to the matter by Miss Margaret Cussans, who was engaged at the time in working out, at my suggestion, the circulation ofGammarus pulex on the living animal under the microscope. We then noticed that this species responded only to the bass note of the College chime, which, giving on examination 240 vibrations per second, therefore corresponded to the B below middle C of the pianoforte. In the first place it must be noted that the animal responds (in water) only when imprisoned in the compressorium or live box. This makes the case the more interesting, since if the reaction had not been observed by the merest accident, the same experiments might have been conducted on the animals in their natural surroundings with absolutely negative results. They are compressed only so much as to prevent wandering, whilst leaving their appendages quite free. They may then be kept under observation on the stage of the microscope. I had a special live box constructed so as to permit a gentle stream of water being passed continuously through it. This prevents asphyxiation, and allows a single specimen to be experimented with for a. longer period than would otherwise be possible. It is, of course, inevitable that the vibrations should be conveyed to the animal by the medium in which it finds itself, and in this sense it is impossible to postulate true; audition (as usually understood) in any true aquatic species. The factor to eliminate here is clearly the specific period of the medium itself, the energetic vibration of which, in response to its own note, may vitiate the result of the experiment. For this reason I used three types of live box and microscope; without, however, any difference in the results being noticed. Further, the fact that the response is only evoked by a limited range of tone, and then without reference to any specific forced or sympathetic vibration of the surrounding medium, intimates that the stimulus is associated with a definite physiological status of the animal itself, since even if the box were an essential factor in the success of the test, we should still leave unexplained the differential response. It is, however, easy to show that the box itself, owing to its small size and heavy construction, is ill adapted for the transmission of vibrations, and is certainly the last means one would adopt to transmit aerial vibrations freely to the animal.