186 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
chitin is either pierced by a pore, or ends in a thin permeable membrane, 
which allows substances in solution to enter the cavity of the hair. If 
found on the first or second antennz, 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 
bair. 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 peripheral 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 unfringed 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 toa 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 hematoxylin 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 55 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 even 
two nerve elements to a hair, the number of fibres or cells must be at 
least twice as large as that of the hairs. 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. 
