186 bulletin: museum of comparative zoology. 



chitin is either pierced by a pore, or ends in a thin permeable membrane, 

 wiiich allows substances in solution to enter the cavity of the hair. If 

 found on the first or second antennse, they are termed olfactory hairs ; 

 when on the oral appendages, taste or gustatory bristles, though their 

 functions are probably the same. 



a. Number of Nerve Elements to a Single Bristle. Until 1891 it was 

 supposed that only a single ganglion cell and fibre-process supplied each 

 hair. Then Vom Rath ('91, p. 207) asserted, that beneath every sensory 

 hair of crustaceans there is a large group of ganglion cells, each sending 

 out a 2>eripheral process, these converging and entering the base of the hair 

 as a single large strand. This opinion he again expressed in 1894 for 

 all arthropods. He did not study the innervation of the otocyst, but 

 apparently confined his attention to the olfactory type of hair, as his 

 figures are all of imfringed bristles. 



The number of elements supplying each hair of the otocyst can be 

 determined by, first, counting the number of fibres in the auditory nerve, 

 and the number of nerve cells connected with these fibres, and then, 

 secondly, comparing the statistics thus obtained with the number of 

 hairs in the otocyst. If there is but a single cell and fibre to a hair, 

 these numbers should coincide, at least approximately. But if there are 

 always numerous elements, as Vom Rath maintains, then the number of 

 fibres and nerve cells should be many times that of the hairs. The 

 number of fibres can be readily counted in a transverse section of the 

 otocyst nerve stained intensely with iron ha^matoxyliu and only slightly 

 decolorized. The ganglion cells can be enumerated in serial sections cut 

 in the plane of the long axes of the cells, so that their characteristic size 

 and bipolar condition (seen in Plate 2, Fig. 6) will readily distinguish 

 them from the hypodermal or matrix cells. From many such counts, 

 the number of nerve elements was found to be approximately equal to 

 that of the hairs. For example, in one otocyst there were 5.5 hairs, 53 

 fibres in the nerve supplying them, and 58 cells connected with these. 

 The number of cells could not be determined with perfect accuracy, as 

 some cells may have been halved in sectioning. Slight variations in the 

 numbers, however, are not of great significance, as, in order to have oven 

 two nerve elements to a hair, the number of fibres or cells must be at 

 least twice as large as that of the haii's. Moreover, the ganglion cells 

 are always isolated, and each is surrounded by a separate sheath ; their 

 fibres are also separated from each other. Neither cells nor fibres occur 

 in groups surrounded by a common sheath as Vom Rath ('92) describes 

 them. In the otocyst, then, there is but one nerve element to each hair. 



