No. 418.] NOTES AND LITERATURE. 859 
expanded by blood pressure. The discharge of the contents of the 
otocyst is through the natural aperture of the cyst, which remains 
open in macrurans but rapidly closes in brachyurans. Where an 
otolith is discharged, as in the shrimp and other macrurans, the ani- 
mal immediately after ecdysis gathers in its claws small sand grains 
and puts them in the opening of the otocyst. These become attached 
to one another and to the auditory hairs by secretions from the walls 
of the otocyst and thus form a new otolith. 
_ The otocyst was originally described as an organ of hearing. 
When sounds are produced under the water of an aquarium in which 
shrimps are contained, the animals respond by a darting movement 
if near the source of sound. The vibrations which stimulate the 
shrimps, however, can be /z// by the submerged hand at a distance 
of ten to twenty centimeters greater than that at which the shrimps 
react. Moreover, shrimps respond to these vibrations even after the 
otocysts are removed. ‘The reactions are inhibited, however, by the 
removal of the antenne and antennules with their tactile hairs. It 
follows from these observations that whether we call the reactions 
auditory or tactile, the otocysts take little or no part in producing 
em. 
If, then, the otocysts are not stimulated by sound, what is their 
function? When the otocysts are removed, shrimps swim with a 
more or less rolling motion and may even turn ventral side up. 
Their equilibration is thus shown to be seriously interfered with. 
When their eyes are covered with opaque materials so as to blind 
ves they swim with little or no rolling motion; but when both 
poo deprived of otocysts, they move with the greatest irregu- 
c uos sometimes on their backs and sometimes in irregular 
em ii Pe eir capacity for orientation has disappeared completely, 
? experiments show, though the eye plays some part in 
keeping the animals upright, the otocyst is the chief sense organ in 
tation reflexes. The otocyst is stimulated through 
Mi Ri the otolith on the sensory hairs, as is shown by the 
cgi So OR of Kreidl, who induced shrimp to form otoliths 
€s instead of sand grains and then found that the 
ani . 
n became oriented to the lines of force of a magnet as they 
fo st y did to gravity. These results are confirmed by Prentiss. 
in the um ment of the otocyst is also dealt with. It is not present 
the second rval stage of the lobster nor is it more than indicated in 
almost the ie third, but at the fourth stage it suddenly appears with 
© full complexity of its adult structure. The locomotion of 
