176 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
of the hypodermis cells elongate to form the matrix cells which later 
produce auditory hairs. The latter are formed only after hatching. 
Herrick (’95) mentions the auditory organ only in connection with 
the development of the lobster. The otocyst becomes prominent at 
the third larval stage, appearing as a shallow depression bordered with 
short setee and containing a few grains of sand. The depression gradu- 
ally enlarges, forming in the fifth stage a sac, the aperture of which 
decreases in size with successive moults, until the adult condition is 
attained. 
Bethe (95, ’97) has traced the auditory fibres of Carcinus menas 
centrally to the neuropil of the first antenna, where they end in 
delicate fibrillations. Some of these fibres may also end in the 
slobulus. 
From this review of the literature, it is seen that little has been done 
on the finer anatomy of the otocyst. Hensen’s work, once considered 
exhaustive, will not suffice at the present time. The organ of Brachyura 
has not been touched upon since Hensen’s dissections, while our knowl- 
edge as to the innervation of the different sensory hairs of Crustacea is 
left in a very hazy, confused state, since the exact condition of the 
peripheral endings is not firmly established, Claus, Vom Rath, Retzius, 
and Bethe each holding different views. The question remains un- 
settled as to whether the manner of innervation is the same for all 
the sensory hairs. G. H. Parker (’90) has clearly shown that the optic 
nerve in Crustacea is highly differentiated ; but all the other sense organs 
have, according to Vom Rath, the same manner of innervation, even 
though they differ in function as much as the so-called auditory and 
olfactory bristles. 
All the investigators of the crustacean otocyst, Bethe alone ex- 
cepted, carried on their work under the impression that they were 
dealing with an auditory organ. This certainly prejudiced them in 
drawing conclusions. But for this, Hensen would never have likened 
the thickened wall of the crab’s otocysts to the malleus of the verte- 
brate ear, nor made other far-fetched comparisons. A comparative 
study of the innervation of the otocyst, especially if supplemented 
by that of the olfactory and tactile bristles and the conditions in 
embryonic stages, cannot fail to clear up some of these questionable 
points. 
