PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 225 
The above experiments were duplicated on Crangon vulgaris with 
similar, though less marked results, as Crangon is much more sluggish 
than Paleemonetes. 
A third set of experiments was tried with Virbius zostericola, a 
shrimp-like decapod without otocysts. Normal animals responded vigor- 
ously on striking a glass jar partially submerged beneath the water in 
which they swam. This response, much increased by strychnine 
poisoning, was distinctly diminished when both antenne and antennules 
were removed. 
e. Meaning of these Experiments. All of my experiments confirmed 
the conclusion of Beer, that free-swimming decapods, whether possessing 
otocysts or not, will respond to stimuli which are transmitted to them 
by the liquid medium they inhabit. The next question is, to determine 
whether this response is caused by the perception of sownd waves or by 
the coarser vibrations or jars imparted to the water. In other words, 
have we to do with true audition or with the sense of touch? 
Beer has clearly shown that there is no such thing as the transmission 
of pure sound waves from air to water. Coarser waves are imparted to 
the liquid simultaneously with those of sound, and can readily be felt 
by the immersed hand. 
After making a number of trials with sounds produced as in the pre- 
ceding experiments, I ascertained that the vibrations not only could be 
plainly felt by the submerged hand, but also that they could be felt at 
a distance from 10 to 20 em. greater than that at which the shrimps would 
react. This fact does not at all prove that the animals experimented 
with do not hear, but merely shows that the responses supposedly pro- 
duced by sound stimuli may be simple tactile reflexes, called forth by 
vibrations which, since appreciable to the immersed fingers, we may cer- 
tainly assume to be felé by these animals, so well supplied with delicate 
tactile organs. 
That the reaction is really due to tactile stimulus rather than to audi- 
tion, is indicated by several facts brought out by the experiments : 
(1) Animals, when near the wall of the vessel, even though distant 
from the source of the sound, respond vigorously, leaping nway from the 
wall and toward the sound. The wall is set into vibration by the pro- 
duction of the sound, and it is apparently this vibration which affects 
them, rather than the true sound-waves imparted to the water. 
(2) The average distance from the source of the sound at which they 
will respond is less than that at which vibrations may be felt by the 
hand. 
