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. Ifan animal happened to be near the side 
of the vessel, and the sound was produced near the opposite wall 40 em. 
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 antenne 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 
the stimulus. The response was usually well marked, a leap of from 10 
to 15 cm. being made. 
b. 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 effectually 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 Antenne and both Antennules. The removal of the 
antennze 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 em. or less) 
to the source of the sound, or in contact with the walls of the vessel, 
would it respond, and then only feebly. Slight 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. 
