216 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Their innervation is also essentially the same. In the vertebrate crista 
an auditory nerve fibre passing from the brain is connected with a bipolar 
nerve cell in the auditory ganglion, from whence its peripheral fibre ex- 
tends to one of the epithelial sense cells, ending with a slight enlarge- 
ment in close proximity to, or in contact with its base. The single fibre 
supplying each end-organ is never directly connected with the cell, nor does 
it ever run through it to the hair itself. The only difference between the 
peripheral endings just described, and those of the otocyst, is that in the 
hairs of the latter the fibres end free in the base of the hollow shaft, at 
the point where, from the structure of the hair, the greatest stimulus 
would be produced ; while in the vertebrate end-organ the nerve process 
is applied to the convex under-surface of the basal cell, which would 
transmit stimuli with an equal degree of intensity to fibres in contact 
with it at any point. 
The otoliths of the vertebrate ear are formed by secretion, while 
those of the crustacean otocyst are largely granules of sand taken into 
the sac from the exterior. In some Crustacea, however, such as the 
Myside, and in many other invertebrates, the otoliths are formed within 
the sac. 
In all decapods the innervation of the otocyst hairs distinctly differs 
from that of the olfactory bristles, not only as to peripheral termina- 
tions, but also in the number of nerve elements supplying each hair. 
As has been previously noted, the stimulus is transmitted by specialized 
cells or hairs to the nerve fibres of both the otocyst and the vertebrate 
ear, and is never applied directly to their endings. In either case only one 
nerve element is usually in contact with the terminal sense cell, and this 
is apparently ample to carry the isolated nervous message to the brain. 
With the olfactory sense it is different; in both vertebrates and 
Crustacea the chemical stimuli which produce the olfactory sensations 
act directly upon the nerve cells or their terminal fibres. In vertebrates 
portions of the nerve cells are exposed at the surface of the olfactory 
epithelium. In crustacea peripheral fibres from the ganglion cells of 
the olfactory nerve end free in the hollow, perforate bristles. In Nereis 
and the earth-worm, Langdon (95, ’00) has shown that the processes of 
the olfactory cells end free upon the surface of the cuticula, and com- 
pletely exposed to chemical stimuli; a similar condition has been shown 
by Lewis (98) to exist in two polychetous worms of the family 
Maldanide. 
The large numbers of nerve elements ending in each olfactory tube 
or bristle of decapod Crustacea may be accounted for by the fact that 
