224 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



slight leap backwards or to one side, if the source of the sound was 

 within a distance of 20 cm. If an animal happened to be near the side 

 of the vessel, and the sound was produced near the opposite wall 40 cm. 

 distant, the response would be, not a darting away from the source of the 

 sound, but a leap back from the side of the vessel toward the source of the 

 sound. Again, if an animal was facing the side of the aquarium with 

 its antennae in close proximity to it, and the opposite wall was sharply 

 tapped with the finger-nail, or lightly with a hammer, the shrimp, as 

 before, sprang away from the side of the vessel toward the source of 

 tlie stimulus. The response was usually well marked, a leap of from 10 

 to 15 cm. being made. 



6. Poisoned with Strychnine. The responses obtained were invariably 

 much stronger and more uniform with animals poisoned by strych- 

 nine in the manner stated above, than with normal shrimps. In other 

 respects they were the same, and served merely to emphasize the results 

 obtained by the first experiments. Blinded individuals showed practi- 

 cally the same reactions, but to make sure that the factor of vision 

 was eS^ectually cut out, the eyestalks of the shrimps in the succeed- 

 ing experiments were all painted. 



c. Both Otocysts removed. Of animals from which both otocysts 

 had been removed, all but one gave a more or less strong response 

 to the sounds conducted into the water in which they were swimming. 

 The reactions were not as marked, nor could they be produced at as 

 great a distance from the source of the sound, as in the case of normal 

 animals. Nine individuals were affected by the stimulus when at a 

 distance of about 10 cm.; the rest, only when in still closer proximity. 

 A slight jar imparted to the walls of the aquarium produced essentially 

 the same responses as the transmission of sound to the water by means 

 of the vibrating pipe or rod. Removal of the otocysts has, therefore, 

 only a very slight inhibitory effect upon the responses called forth by 

 sound-wave stimuli in normal or strychnine-sensitized animals. 



d. Removal of Antennce and both Antennules. The removal of tlie 

 antennse and antennules, which bear large numbers of delicate tactile 

 hairs, very much reduced the reaction of the shrimps to these vibratory 

 stimuli. Only when an animal was in close proximity (5 cm. or less) 

 to the source of the sound, or in contact with the walls of the vessel, 

 would it respond, and then only feebly. S]it,'ht jarring of the aquarium 

 produced no reaction, unless some part of the animal's body directly 

 touched the sides or bottom of the jar, or was in contact with the sound- 

 producing instrument. 



