190 BULLETIN: MUSEUM OF COMPAKATIVE ZOOLOGY. 



shrimp niuults once iu two or three ruouths, this menus that for nearly 

 halt' the time the nerve tibre cannot extend iurther tiiau the base of the 

 hair. Yet the animals are apparently as sensitive to stimuli duriuo- this 

 period as at any other. After the new hair is fully formed, and its tip 

 projects into the base of the old 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 invagiuated (Plate 3, Fig. 10, tb. set.), 

 they may be traced some distance into the shaft of the ?iew hair. Now, 

 by removing with a fine needle the old test, eta., 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 — cei'tainly of great impor- 

 tance — which occur in all Crustacea between moults. 



At certain stages in their formation the delicate protoplasmic pro- 

 cesses iu 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. 



c. Central I'erminatlons. 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. Wliole preparations of the anten- 

 nules and brain could be used for this jJurpose, as the tissues wore 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 tlie sensory hairs 

 in tlie floor of tiie otocyst, forms the sensory ganglion, and iu continuing 

 its course approaches somewhat the luedian 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 



