PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 203 
a. Number of Nerve Elements to a Single Bristle. The number of 
cells and fibres for the whole ‘sac could not be determined with exact- 
ness, as other sensory elements, supplying tactile hairs, are mingled with 
those of the otocyst. But in the short transverse row of large hairs, 
the cells and fibres are sufficiently isolated to allow of their being 
counted in serial sections. There are but nine hairs in that row, and if 
the nerve elements supplying them were twice as numerous, it would be 
at once apparent. The cells always occur singly, and their fibres run 
separately and parallel with one another to the bases of their respective 
hairs (Plate 7, Fig. 33). The number of each was counted many 
times, and it is certain that the number of ganglion cells and peripheral 
Jibres exactly equals the number of hairs. Whole preparations of these 
nerve elements stained with methylen blue gave regularly nine ganglion 
cells and fibres supplying the nine sensory hairs. In these few otocyst 
hairs, at least, there is, then, but a single nerve element supplying each. 
In the tactile hairs of the scaphognathite of the second maxilla, many 
methylen-blue impreguations gave conditions like that shown in Figure 
34 (Plate 7), only one sensory nerve element being stained. In the 
short spike-shaped bristles found on this same appendage, from three 
to five ganglion cells (Plate 7, Fig. 32, cl. gn.) were usually found sup- 
plying each bristle. 
In the olfactory bristles of the antennule, the conditions were the same 
as those already described and figured for Palemonetes, though fewer 
elements compose each spindle-shaped group of cells. 
b. Peripheral Terminations. No. branching of peripheral nerve 
fibres was observed in any sensory elements, though many were 
traced the whole length of an appendage. In Cambarus the fibres 
end always at the base in the otocyst hairs (Plate 7, Fig. 33). There 
is often a marked increase in the diameter of the fibre near its termina- 
tion, caused either by the staining of its sheath at this point, or by a 
partial separation of the component fibrille. Tactile hairs show similar 
conditions in their nerve endings (Plate 7, Fig. 34). 
The fibre strands of the olfactory bristles were, on the contrary, traced 
into the shaft some distance, where they apparently end free. Thus in 
the crayfish, we have a distinct difference in the innervation of the two 
types of sensory hairs, which serves to confirm the statements made 
ecncerning the conditions in Paleemonetes and Crangon. 
e. Central Terminations. The otocyst nerve in Cambarus is large 
enough to be dissected out and traced to the ventral side of the brain, 
which it enters lateral to the larger antennular nerve. Its point of en- 
