184 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Aside from its general interest, this peculiar method of forming the 
new hair is very important, as throwing light on the peripheral endings 
of the nerve fibres in the sensory hairs. By it certain conditions may 
be explained. At each moult the nerve fibres lose their counection 
with the old hairs, and come into relation with new ones. How these 
changes are brought about can best be described in connection with the 
innervation of the otocyst. 
e. The Otoliths are borne in a rather compact mass upon the inter- 
laced tips of the sensory hairs (Plate 1, Fig. 3, ot’/th). They consist of 
irregular grains of sand mingled with other fine mineral particles and 
organic detritus. The largest measure from 8 to 12 uw in longest dimen- 
sion. That the greater part of them are siliceous is shown by their 
insolubility in strong sulphuric acid, and by the fact that they scratch 
glass when crushed upon it. They are renewed after each moult, 
for the freshly formed sac is at first without them. New otoliths are 
pushed in by means of the chele through the aperture of the sac 
while its walls are yet so soft and flexible as to admit quite large grains 
of sand. By watching animals soon after moulting it can be observed 
that they stir up the sand at the bottom of the aquarium in which they 
are confined ; as soon as some particles have come to rest upon the 
dorsal side of the antennule, one or both chele are raised, and by their 
tips the grains of sand are pushed back under the protecting lid of the 
opening into the otocyst. Otocysts from which most of the sand parti- 
cles had been carefully removed by forcing a jet of water into the sac 
were found after a lapse of two days to contain otoliths derived from 
iron filings which had been strewn on the bottom of the aquarium. The 
otoliths are often entangled in the feathery plumes of the auditory hairs, 
and are in this case attached to them by an organic substance, which is 
probably secreted by unicellular glands situated beneath the floor of the 
sac. No multicellular glands, such as are found in the lobster and cray- 
fish, could be detected beneath the otocyst of Palemonetes. Very 
minute canals, which are probably the ducts of gland cells, were found 
running through the chitin wall and some distance into the tissues | 
beneath ; they were very clearly brought out, and their tubular condi- 
tion proved beyond a doubt, in silver preparations, and in those made 
with lead formate; but unfortunately their connection with gland cells 
could not be demonstrated. The functions of the otolith and the 
part it plays in audition, or equilibration, will be discussed in the 
experimental portion of this paper. 
