CRUSTACEA. 
275 
nothing but common sand, which he has observed introduced by 
the free will of the animal, and is repeated after every moult ; 
but in those Crustacea in which the auditory chamber is closed, 
the otolithes, which are cast at every successive moult also, are 
again reproduced; these, from thier behaviour with chemical 
reagents, Prof. Himly, who tested the substance of 200 stones for 
the author, thinks to be fluate of calcium. He next treats of 
the auditory chamber and the auditory hairs, of which three 
kinds are distinguished: — 
1. Hairs attached to the otolithes. 
2. Free hairs of the auditory chamber. 
3. Auditory hairs situated on the external surface of the 
animal. 
The first exists chiefly among the macrurous Decapoda, in 
some cases springing from among the otolithes, in others sup- 
porting, as in the tail of MysiSy the otolithe in its position. 
The second kind of hair exists in the auditory chamber of 
the Brachyurous Decapoda, whic h contains no otolithe, but a 
chamber filled with a fluid, in wliit.h these hairs stand in great 
numbers. 
The third kind exists on the peduncle of the first antenna, 
and on the second joint of the second antenna, and, in Palcemony 
on the rami of the posterior pair of pleopoda. In My sis the 
auditory apparatus is situated on the inner ramus of the posterior 
pair of pleopoda ; so that the function of hearing must be con- 
sidered as established in this part of the body. He also found 
them on Gebia ; but he found no auditory hairs on any other 
part of the animal. In Palasmon squilla the auditory hairs are 
replaced, as the animal increases in age, by those of the ordinary 
kind. 
Among the Brachyurous Crustacea there are no otolithes, but 
a complicated calcareous chamber, as first described by us in the 
^ Annals of Nat. Hist. ^ for 1855, within the first joint of the 
peduncle of the first antenna, the cavity of which Dr. Hensen 
says is provided with hairs. 
After describing the form and structure of the auditory hairs, 
as well as the different character of apparatus in distinct groups 
of Crustacea, he classifies them under the following heads : — 
1. Those which have one otolithe within the auditory cham- 
ber, as Lucifer y SergesteSy Mysisy Hippolyicy and Masti- 
gopus. 
2. Those which have no otolithe and no auditory chamber, as 
Alirntty ErichthuSy Phyllosomay ThysanopodUy and Pandalus. 
3. Which have a chamber with numerous otolithes, as Palm- 
moriy PasiphaCy CrangoUy AlpheuSy AstacuSj Gebia, Pagurus, 
PalinuruSy Nephrops, and Lithodes. 
4. Which have a closed auditory chamber, but no otolith, 
as Porcellana?, Hippa, Pinnotheres, Myctiris, Ocypoda, 
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