PEEXTISS: 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 Eath'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 Palsemonetes 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 hsematoxylin 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 ^u in diameter. 

 In Figure 13 only a few of the elements are shown ; the sheath, which 

 surrounds hoth 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 explam 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 



