PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. aa 
motions, but when, in addition to this, both otocysts were destroyed, 
compensatory movements completely disappeared. 
Bethe (97), in his physiological work on Carcinas mzenas, confirms 
Clark’s results. Ina previous paper he (’95*) observes that Mysis can 
hear after the otocysts have been destroyed, but with difficulty ; also that 
the animals are more sensitive to low tones than to high. 
Thus, until 1898 three views were held as to the function of the 
otocysts : 
(1) That they are purely auditory organs (Hensen and the earlier 
zoOlogists). 
(2) That they are both auditory and static in function (Delage and 
Bethe). 
(3) That they are purely static in function, i. e. organs of orientation 
(Kreidl, Clark, and others). 
‘To determine whether decapod Crustacea really hear, and if so, 
whether the otocyst is the organ of audition, is the aim of two papers 
by Beer (’98, ’99). 
In criticising the conclusions reached by Hensen and Bethe, Beer 
remarks in his first paper that, because decapods were made to react to 
different sounds, does not prove that these Crustacea responded to true 
sound, or that they heard. These reactions may have been due to their 
feeling vibrations transmitted to the water from the walls of the vessel 
in which they were confined, —a tactile reaction, or, to use Bethe’s term, 
a “tango-reflex.” Experiments with sounds produced in the air Beer 
considered superfluous, as it is a well-known physical fact that most of 
the sound waves are reflected from the surface of water. 
Beer found that Crustacea reacted strongly to sounds produced in the 
water by striking partially submerged bells, jars, etc., but only when 
they were not at a greater distance from the source of sound than that 
ut which vibrations could be detected by the hand immersed in water. 
The animals responded more strongly when near the walls of the vessel ; 
but vibrations could be felt by the hand also in this position more dis- 
tinctly, even though further removed from the source of the sound. 
For animals well supplied with tactile organs, he regards pure sound 
or pure audition as impossible; because vibrations could be felt as soon 
as heard, and, this being the case, audition would be useless. 
On removal of the otocysts, Palemon and Palemonetes still responded 
to sound waves produced in the water. There was, however, a slight in- 
hibition of the customary reactions, therefore the hairs of the otocyst 
are probably slightly tactile as well as static in function. 
