238 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the animal otherwise to regain its normal condition. Even if placed at 
once in filtered water, some otoliths soon make their appearance, probably 
originating from the excreta of the animals themselves. 
In lobsters the larve regain their normal condition within a much 
shorter interval after ecdysis than do adult individuals ; their digestive 
tract is also much less likely to contain material suitable for the forma- 
tion of otoliths. Therefore, after trying in vain to completely remove 
the otoliths from the sacs of Crangon and Palemonetes, my attention 
was directed to lobster larvee as much more favorable material than 
the adult shrimps. As they moult at intervals of a few days, it is also 
much easier to obtain them directly after ecdysis or in the very act 
itself. So obtained, and placed at once into filtered sea water, larve of 
the fourth stage may be kept without otoliths for from twenty-four to 
forty-eight hours, and a favorable opportunity is thus given for observing 
the effect produced, by the lack of otoliths on the equilibrium of the 
animals. 
Observations were made on eighteen larve of the fourth and fifth stages, 
all of them being kept free from otoliths for at least twelve hours. Within 
two hours after moulting most of them swam about actively, and ate 
greedily when fed with bits of crab’s liver. In swimming, however, they 
show distinctly the phenomena manifested by shrimps which have been 
deprived of their otocysts. There is both “rolling” from side to side, 
and ‘“ pitching” forward and backward; often they swim with the 
ventral side uppermost. Much more easily overturned than normal 
larvee, they do not right themselves at once, but if turned upon the 
back, will continue to swim in that abnormal position. If blinded, 
the loss of equilibrium is still more marked. All these conditions 
are in strong contrast to the actions of the normal free-swimming larve 
of these stages, which conduct themselves in the characteristic manner 
already described for Paleemonetes. 
The observations having been made and recorded, the animals were 
killed, and the otocysts dissected out and examined under the micro- 
scope. Scarcely a particle of inorganic matter was found in the sacs 
of sixteen larve. In two individuals a few small grains of sand were 
found in one otocyst, but the other was entirely destitute of otoliths. 
From the number of cases observed it seems safe to conclude that the 
otoliths do play an important part in equilibration, and that it is the 
pull of gravity upon them which stimulates the sensory hairs of the sac. 
If the loss of the power of accurate orientation were to be attributed to 
the abnormal conditions resultant upon ecdysis, it might be said in 
