PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 199 
Leaving the anterior end of the brain with a bend away from the 
median plane, it gives off in front of the globulus a small lateral branch 
(rm. l.), which supplies the tactile bristles of the antennule. The main 
nerve, after passing between the globulus and the posterior end of the 
sac, runs forward only a short distance to the sensory prominence on the 
lateral side of which its ganglion lies. The peripheral fibres can be 
traced forward and slightly mediad from the ganglion to the bases of the 
otocyst hairs. The whole course of the nerve is approximately in a 
frontal plane, though its peripheral ending is slightly more ventral than 
its point of departure from the central organ. In Figure 28 (Plate 6) the 
transverse section of the antennular nerve (x. at.) is seen to be median 
to the sac, while the ganglion cells of the otocyst nerve (cl. gn.) are 
lateral to it. 
a. Number of Nerve Elements to a Single Bristle. There is in Crangon 
but one ganglion cell and fibre to each otocyst hair. The cells and fibres 
were counted as in Palemonetes, and the numbers thus obtained were 
found to agree approximately with the number of the hairs. 
Methylen-blue preparations of the olfactory nerve elements were 
obtained, and the conditions there brought out agreed essentially with 
those found in the same type of hair in Palzmonetes, large groups 
of nerve cells being present beneath each olfactory bristle. 
b. Peripheral Terminations. Nerve fibres to otocyst hairs were 
never traced beyond the enlarged base of the bristle, where they end free 
without branching. A typical nerve element of the otocyst is given 
diagrammatically in Figure 29; it shows the peripheral ending of the 
fibre at the base of set. ot. 
In the olfactory hairs, on the other hand, the nerve fibres in most 
cases could be traced up into the shaft of the hair, though never through 
its whole length. Thus in Crangon, as in Palemonetes, there is a 
distinct difference in the innervation of the two types of bristles, both as 
to the number of elements, and in the manner in which the fibres end. 
c. Central Terminations. Centrally the otocyst nerve ends in a posi- 
tion (Fig. 29) corresponding to that of the central terminations in Pal- 
emonetes, but the fine fibrillar branching, which was brought out 
distinctly by methylen blue in that form, could not be impregnated in 
Crangon. 
d. Histology of the Nerve Elements. So far as worked out, this was 
similar to that already described in Palemonetes. A myelin sheath is 
present in Crangon as well as Paleemonetes, though it was not observed 
in any other decapods. 
