PRENTISS: THE OTOCYST OF DECAPOD CRUSTACEA. 187 
In the tactile hairs the same methods of procedure were followed ; and 
further evidence was obtained from methylen-blue preparations. One 
of these is shown in Figure 11 (Plate 3). It will be observed at once 
from this figure that there is only one cell and one fibre to each hair. 
But in other preparations of the same appendage (Plate 4, Fig. 14) from 
two to ten cells are found grouped together irregularly, and sending all 
their processes to the same bristle. When this was the case, it was 
always observed, that the hair so supplied was of the short, blunt, fringeless 
type, and so possibly not a tactile but an olfactory hair. 
So far, the evidence has been entirely against Vom Rath’s statement ; 
but if we examine the innervation of the olfactory bristles, entirely differ- 
ent conditions will be found to exist, and in complete accord with his 
conclusions. 
On the inner flagellum of the first antenna of Palemonetes numerous 
olfactory bristles are found, arranged in rows of four or five hairs each 
(Plate 4, Fig. 13). The nerve cells and fibres supplying these hairs 
stain beautifully with methylen blue. Only single elements at first 
appear, but if the stain is allowed to act for a longer period, nearly every 
cell and fibre will become impregnated. It can then be seen that a large 
number of elements supply each hair. The cells are packed so closely 
together as to make the counting of a group difficult, but many counts 
upon sections stained in hematoxylin make it certain that more than a 
hundred cells may compose a single group, and supply a single olfactory 
hair. The cells send off each a peripheral fibre. These fibres enter the 
base of an olfactory hair as a single large strand, 12 to 15 w in diameter. 
In Figure 13 only a few of the elements are shown ; the sheath, which 
surrounds both cells and fibres, marks the outline of the spindle-shaped 
group of cells, and shows the size of the fibre strand. 
The gustatory hairs on the oral appendages are also each supplied 
with numerous nerve elements (Plate 4, Fig. 14). The number is 
not nearly so great as in the olfactory hairs, —averaging about 10 to 
a hair, —nor are they so regularly and compactly grouped, They differ 
markedly, however, from the conditions found in tactile and otocyst 
hairs. 
The distinctly different conditions —as regards the number of nerve 
elements of the hairs— found in the olfactory and otocyst bristles, seem 
to explain the diverse conclusions of Bethe and Retzius on the one hand, 
and Vom Rath on the other. The two former observers worked on the 
tactile type of sensory bristles, while Vom Rath, as his figures show, 
evidently confined his attention to the other type. The conditions which 
