1910.] 



Tone Perception in Gammarus pulex. 



395 



which time, the animal failing to respond even to the B flat, the experiment 

 was brought to a conclusion. 



A large number of specimens were tested with a view to ascertaining 

 whether the sensitiveness to middle B flat was of general occurrence. 

 For example, a male placed on the resonator responded moderately to A flat 

 at the first stimulus, but very slightly if at all to the same note the next 

 four times. Tried then with B flat and A flat sounded alternately, five 

 times each, there was always a response to the B flat, quite distinct if not 

 very well marked, but none at all to the A flat. The subordinate notes may 

 be eliminated by gradually withdrawing the trombone to a distance. Thus 

 a male on the resonator responded quite well when the bell of the 

 instrument was 4, 7, and 10 inches from the mouth of the resonator, 

 but did not respond at all after the foot had been passed. In another case 

 there was a marked response when the bell was a foot away, and even slight 

 responses at 1^ and 2 feet, but none beyond the latter distance. In a 

 female, with the bell at a foot, there was a marked response to B flat, and 

 only a slight one to A natural. Again, a female tested on the physical table 

 responded distinctly to B flat at 4 inches, slightly at 8 inches, but distinctly 

 again at 12 inches, and at 2 feet not at all. Eeturning now to 4 inches 

 there was a well-marked response, and immediately at 2 feet a slight 

 response. 



A specimen in a remarkable condition of hypersesthesia was encountered 

 on one occasion. In the first experiment the chromatic scale was played 

 with one minute rest between successive notes, but it should be pointed out 

 that at first the animal also responded to the slightest tap on the resonator, the 

 only individual which has done this. It was a male, and we tried it first on 

 the resonator at 135 cm., and with the current of water. The result was as 

 follows : To middle B flat and A natural there were at once very striking 

 and emphatic responses ; to A flat and G, rather less ; to F sharp, F, 

 E natural, and E flat, well-marked responses ; to D natural, D flat, and C, 

 not so well marked. We now repeated the same scale, but only allowed 

 sufficient time between each note for the antennae to straighten out. It 

 responded in the same way to every note as before, but not so vigorously 

 Tested with the chromatic scale up from middle B flat, and with the same 

 minute intervals, we found : B flat and B natural, well marked ; C, less ; 

 D flat, very slight, hut responded well to the middle B flat immediately; 

 D natural and E flat, slight, but only slight to the B flat also ; E natural, 

 slight, but a better response to the B flat ; F, very slight, but a much better 

 response to the B flat. In the latter experiment the animal was, I think, 

 probably becoming fatigued, and thus did not respond as well as it might 



