190 - BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
shrimp moults once in two or three months, this means that for nearly 
half the time the nerve fibre canuot extend further than the base of the 
hair. Yet the animals are apparently as sensitive to stimuli during this 
period as at any other. After the new hair is fully formed, and its tip 
projects into the base of the ojd hair, which has now lost all direct 
nerve connection, the animals still respond quickly to tactile stimulus ; 
the impulse resulting from the stimulus is transmitted from the tip of 
the old hair to its base, thence to the shaft of the new hair, by which 
in turn it is transferred to the nerve fibre. 
(3) If certain of the nerve fibres supplying the tactile hairs are 
stained with methylen blue just before ecdysis when the new hairs are 
fully formed but still deeply invaginated (Plate 3, Fig. 10, 7. set.), 
they may be traced some distance into the shaft of the xew hair. Now, 
by removing with a fine needle the old test, cta., the new hairs can be 
pulled out into their functional position. The nerve fibres, however, are 
not pulled out with the hair the whole distance, but remain nearly in 
their original relative positions, barely projecting into the bases of the 
hairs, a condition already pointed out in Figure 11 (Plate 3). 
It is unfortunate that the investigators of these nerve endings have 
never taken into account the tissue changes — certainly of great impor- 
tance — which occur in all Crustacea between moults. 
At certain stages in their formation the delicate protoplasmic pro- 
cesses in the tips of the new hairs stain very sharply, and have a 
varicose appearance, similar to that of nerve fibres; as these project 
some distance into the old hairs, they might easily be mistaken for 
terminal nerve endings. 
ce. Central Terminations. By means of methylen-blue preparations the 
nerve fibres supplying the otocyst were traced continuously in their course 
from the sac to their central endings. Whole preparations of the anten- 
nules and brain could be used for this purpose, as the tissues were ex- 
tremely transparent. On account of the proximity of brain and otocyst, 
the nerve supplying the latter is very short. It enters the anterior end 
of the brain lateral to the antennular nerve, the two joining as they 
pass within (Plate 3, Fig. 12). While the antennular nerve pursues 
a straight course, the other (Figs. 2, 4) descends from the sensory hairs 
in the floor of the otocyst, forms the sensory ganglion, and in continuing 
its course approaches somewhat the median plane and describes the 
form of an elongated letter S, the plane of which is dorso-ventral. 
Just before the two nerves unite to enter the brain, a third smaller 
