188 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Vom Rath found in the olfactory type he too hastily attributed to all 
the sensory hairs of Crustacea, 
b. Peripheral Terminations. Here again we find a difference of opin- 
ion. Hensen (63, p. 368) asserted that the peripheral fibre was 
attached to a process (ingula) from the base of the hair shaft. Claus 
(91), Vom Rath (92, ’94), and Bethe (’95) found fibres reaching to the 
very tip of the sensory bristles; while Retzius (’95, p. 17) found no 
evidence of nerve terminations beyond the enlargement at the base of 
the hair in decapods, though he observed in Hntomostraca the same con- 
ditions as did the other three investigators. 
I have obtained hundreds of preparations of nerve endings in the 
various sensory hairs of Palemonetes with several of the best modern 
nerve methods, and all furnished the same evidence. The conditions 
found for otocyst hairs were in every case as illustrated in Figures 4 
and 8 (Plates 1, 2). The ganglion cells, as already noted, lie at some 
distance (0.25 to 0.40 mm.) from the bases of the hairs which they supply. 
The reason for this becomes obvious, when the formation of the new 
hairs is considered. The developing hair tube extends below the base of 
the old hair a distance equal to at least one-third the length of the hair, 
and the ganglion cells necessarily lie below the lower or proximal end 
of the hair tube (Plate 3, Fig. 10, tb. set.). Hence they must be at least 
a third the length of the hair distant from its base, though they occupy 
a closer position directly after ecdysis than for some time before. The 
terminal fibres (Plate 2, Fig. 8, fbr. n.), which are as long as the dis- 
tance of their cells from the hairs, enlarge slightly as they near their 
termination, and always end in the expanded base of the hair directly 
below the shaft proper. There are no signs of attachment to any part 
of the wall of the hair, nor of fine branching of the distal end of the fibre, 
such as Retzius (’90) describes. Figure 4 (Plate 1) shows diagram- 
matically one nerve element of the otocyst, the position of the ganglion 
cell, and the ending of its peripheral fibre in the base of the hair. In 
Figure 8 (Plate 2) only the termination of the fibre, highly magnified, 
is given. 
The elements of the tactile hairs end in precisely the same manner as 
those of the otocyst. A number of these endings are shown in Figure 
11 (Plate 3). In no case was a nerve ending demonstrated in the shaft 
of the hair. Thus, all the evidence of preparations goes to prove that 
in both otocyst hairs and tactile hairs the nerve fibre, without branching, 
ends in the enlargement at the base of the hair, and never enters the shaft 
itself. 
