PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 191 
nerve is received by the otocyst nerve on its dorsal side (Plate 1, 
Fig. 2, rm. /.). This nerve is formed by an aggregation of fibres from 
the tactile bristles of this segment of the anteunule, and runs almost 
straight toward the median plane till it joins the nerve of the otocyst. 
The fibres of the latter enter the anterior end of the brain ventral to 
the optic neuropil, and median to the’ globulus (Plates 1, 3, Figs. 
4, 12); they extend backward to near the posterior end of the central 
organ in an almost horizontal plane, lateral to the fibres of the antennular 
nerve. They end in a region just anterior and median to the neuropils 
of the second antenne, branching into delicate dendritic fibrille, which 
form a well-marked neuropilar mass (Fig. 12, for’.). 
Fibres supplying the tactile hairs of the basal segment of the anten- 
nule end in the same neuropil, while the main nerve to the antennule 
ends in a closely connected fibrillar mass just median to it. No nerve 
cells were found in the brain connected with the sensory fibres from the 
otocyst. Association elements, with large dendritic branches, put these 
newropils into communication with the optic centres. One of these con- 
necting fibres is shown in Figure 12 (for. ass.). Its cell, which sup- 
posably exists, was not stained. According to Bethe’s (’97, Taf. xxviii. 
an.1) experimental work on the brain of Carcinus menas some of the 
otocyst fibres should end in the globuli. He could not demonstrate 
such fibres, however, in his preparations of the erab’s brain, nor was I 
able to obtain conclusive evidence of such endings in the globuli of 
Palzemonetes. 
d. Histology of the Nerve Elements. The nerve fibres of Pale- 
monetes are relatively large ; those of the otocyst reach their greatest 
size immediately before they enter the neuropil substance of the brain. 
At that point in their course they are from 3 to 5p in diameter, not 
including the nerve sheath. In a transverse section of the nerve the sep- 
arate fibres show distinctly, as they are held apart by connective tissue. 
The fibrillar structure was made out definitely only in methylen-blue 
preparations which had been well differentiated in process of fixation. 
The gold-chloride method of Apathy, though tried several times, did 
not give a successful reaction. Fibrille were made out distinctly in 
only one preparation, though some evidences of such structure appeared 
in many. Figure 15 (Plate 4) shows a portion of a peripheral fibre in 
which many fibrils are seen ranning longitudinally. No single fibril 
was traced any considerable distance, nor could any evidence of the 
fibrils be found in the ganglion cells. The fibrille are embedded in a 
