188 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



Vora Eath fouud iu 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 {lingula) from the base of the hair shaft. Glaus 

 ('91), Vom Rath ('92, '94), and Bethe ('95) found fibres reaching to the 

 very tip of the sensory bristles; while Eetzius ('95, p. 17) found no 

 evidence of nerve terminations beyond the enlargement at the base of 

 the hair iu decapods, though he observed in Entomostraca 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 Pal«monetes 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 oue-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, ib. set.). Hence tliey 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. 7i.), 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, xoithoiit branching, 

 ends in the enlargement at the base of the hair, and never enters the shaft 

 itself. 



