1893. BIOLOGICAL THEORIES. 427 
in close relation with a large nerve ganglion, or rather pair of nerve 
ganglia, with which the eyes and tentacles are also connected. The 
organisation of the mollusc is, moreover, incomparably higher than 
that of the jelly-fish, and it is not very rash to suppose that in this 
case the shaking of the animal by the movement of the water, and 
the consequent collision of the walls of the ‘‘ otocyst ” with the lithite 
(‘‘otolith”’) gives rise to a sensation. Whether it does so or not is, 
however, of little moment. The ganglia are connected (indirectly) 
with muscles, and the stimulus produced by the collision of lithite 
and otocyst-wall may safely be assumed to lead to muscular move- 
ments, either reflex or voluntary—movement which will take the 
animal to safer zones of water. 
A shaking of the ‘“‘ auditory sac” of a crustacean would, by 
jolting the “ auditory ” hairs against the lithites—mere sand particles 
—produce a stimulus. The shaking might be produced in either of 
two ways: it might arise from a tremor of the ground upon which, 
or in which, the animal is resting, or from a disturbance of the water 
about the flagella of the antennule. Of the advantage of being thus 
warned of the approach of an animal which either may serve as. food 
for the crustacean, or might feed upon it if it were taken unawares, 
there need be no doubt. ~* 
REFERENCES. 
1. Lamb, H.—‘ A Treatise on the Mathematical Theory of the Motion of Fluids.”’ 
Cambridge, 1879. 
2. Basset, A. B.—‘‘ A Treatise on Hydrodynamics.’’ Cambridge, 1888. 
3. Romanes, G. J.—“‘ Jelly-Fish, Star-Fish, and Sea-Urchins.” London, 1885. 
¢. Hersear Hursr: 
A CORRECTION :— 
In the previous article in this series (p. 352, 19 lines from the bottom), for 
“* 500 miles” vead ‘‘ 500,000 miles.” 
