176 bulletin: museum of compaeative zoology. 



of the hypodermis cells elongate to form the matrix cells which later 

 produce auditory hairs. The latter are formed ouly 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 setae 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 msenas 

 centrally to the neuropil of the first antenna, where they end in 

 delicate fibrillations. Some of these fibres may also end in the 

 globulus. 



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, Yom Rath, Eetzius, 

 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 Yom 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. 



