36 NERVOUS SYSTEM AND SENSE-ORGANS 
That the otocysts are concerned with equilibrium and adjustment 
of movement has been definitely proved by experiments upon the 
Prawn (Palemon). When this creature moults it sheds not 
only the defensive armour of the body but also the lining of 
the otocysts, getting rid at the 
same time of the sand grains. 
which serve as otoliths. Under 
ordinary circumstances _ these 
would be replaced by a fresh 
supply of the same material, but 
Sats the specimens experimented upon 
Fig. 1045.—Otocyst of Lobster (a) in longitudinal sec- ; : : 
tion, enlarged and diagrammatic; sensory bristlesareseen Were Only provided with iron 
proentng in fs cavity, which cntina nomerue lings, some of which in due 
course were introduced into the 
otocysts. It was then found possible by means of a magnet to 
move the particles in various ways, and as a result of this the 
Prawns could be induced to assume all sorts of positions, under 
the impression, so to speak, that they were falling over in this 
or that direction, which they would have been if the shifting of 
the otoliths had been produced by ordinary causes. 
ANTENNULE 
Fig. 1046.—Opossum Shrimp (J/yszs), cnlarged. One of the otocysts (Ear) is seen in the tail 
{n one Crustacean, the Opossum Shrimp (JZyszs), the otocysts, 
in this case closed, are lodged in the flaps of the tail-fin, but why 
they should have this position is not known (fig. 1046). 
It is generally assumed that animals which are endowed with 
a voice or its equivalent also possess powers of hearing, at least 
if the voice is used for the benefit of one another. Since some 
