PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 213 
b. Peripheral Terminations. As seen in Figure 53 (Plate 10), the 
terminal fibres going to the thread hairs enter the pore at the base of the 
cup-shaped depression, pass up into the enlargement of the hair shaft, 
and there end free. In fact, there is in these hairs no functional neces- 
sity for the further continuance of the fibre into the shaft. Since the 
hairs project free into the liquid of the sac, if the otocyst is jarred or 
tilted, the shaft does not itself bend, but sways backward and forward 
upon its base. It is therefore at the base that the stimulus must mani- 
fest itself, and it was there in every case that the fibres were found to 
end, 
In the olfactory hairs, on the other hand, the nerve fibres continue up 
into the large hollow shafts for some distance (Plate 10, Fig. 52, set. olf). 
The olfactory hairs of Carcinus thus differ in their innervation from those 
of the otocyst, both in the number of nerve elements supplying each hair, 
and in the peripheral nerve endings. In the bristles of the otocyst there 
is but a single nerve element, and it ends free at the base of the hair 
without branching. In the olfactory hairs there may be a hundred ele- 
ments or more which end in the shaft of a single hair. 
e. Central Terminations. Entering the brain in front of, and just 
median to, the globulus, and ventral to the optic centres, the fibres of 
the otocyst nerve run straight back and enter the fibrillar mass (Plate 
10, Fig. 55, n’pil. at.1), called “the neuropil of the first antenna” by 
Bethe (’97), who has described the central endings of the antennular 
nerve of Carcinus. ‘The fibres of the antenuular nerve end in a connected 
neuropil just median to those of the otocyst. Bethe judged from his 
physiological experiments that there should be certain fibres from the 
otocyst ending in the globulus. He was not able to demonstrate such 
endings with methylen blue, nor was there any evidence of their exist- 
ence in my preparations. According to Bethe the fibres from the oto- 
cyst end by the separation of their fibrille in the neuropil. Lack of fresh 
Carcinas material prevented the verification of his work, but I have 
described similar conditions in the shrimp and crayfish. 
d. Histology of the Nerve Elements. As the finer structure of the 
elements of the central nervous system has been fully described by Bethe 
(98), it is unnecessary for me to say anything on that matter, and 
only a few words need be added here as to the histology of the peripheral 
nerves and cells. The peripheral nerve fibres are much smaller than 
in Paleemonetes or Crangon, and are without.a myelin sheath. The 
peripheral ganglion cells are relatively large, averaging 12 u in diameter. 
They are of the typical bipolar form, and are much elongated (Plate 
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