170 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The first good description of the organ, accompanied by figures, was 
given by the Englishman Farre (’43), who carefully dissected the 
otocysts of the crayfish (Astacus fluviatalis), the European lobster 
(Astacus marinus), the hermit crab (Pagurus), and the rock lobster 
(Palinurus quadricornis). 
The organs were found by Farre to be situated in the basal segment 
of the inner antenn (antennules), the thin dorsal membrane of which 
in A. marinus he compared to the fenestra ovalis of the vertebrate ear. 
The openings of the sacs were always found to be large enough to admit 
the otoliths, which rest upon auditory bristles. The otoliths were, he 
maintained, merely grains of sand. The auditory bristles were briefly 
described, and their semi-circular arrangement noted; a nerve was 
traced from the brain to the ventral surface of the otocyst, where it 
formed a plexus. In Farre’s opinion separate fibres probably supplied 
the bases of the different hairs. While the otocysts of the lobster, 
crayfish, and hermit crab were of relatively large size, nearly filling the 
basal segment of the antennule, their openings were very small and 
well guarded by a “chevaux de frise” of bristles. In Palinurus the 
organ was apparently degenerate ; the sac small, shallow, with very large 
opening, and the auditory hairs sparse and irregularly arranged. The 
otoliths were of large size and few in number. The whole apparatus 
was held by Farre to be a delicately modified tactile organ, and he 
doubted if a true auditory function could be ascribed to it. 
During the next twenty-five years otocysts were discovered and ex- 
amined in various decapods by Souleyet (’43), Von Siebold (44, 748), 
Leuckart (’53, ’59), Frey und Leuckart (47), Huxley (51), Leydig (’55, 
’57, 60), Bate (’55, ’58), Hensen (63), Sars (’67), and Lemoine (68). 
Leuckart und Frey (47) briefly described the sacs which they found in 
the endopod of the last abdominal appendages of Mysis, mentioning 
the otolith and auditory hairs. 
Leuckart (’53) made a comparative study of the otocysts in many 
crustacean forms. He divided them into two groups : — Those having 
(1) closed sacs with one otolith, and (2) open sacs with many otoliths. 
Leuckart’s general descriptions agree with those of Farre. 
Kroyer (’59) devotes a few pages of his monograph on Sergestes to 
a comparative account of this organ in different Crustacea. He follows 
Leuckart’s method of grouping. To the first type (closed sacs, and one 
otolith) belong such forms as Lucifer, Sergestes, Mysis, and Phyllosoma. 
In the second group (open sacs and many otoliths) are placed Homarus, 
Astacus, and Palinurus. In the opinion of Kroyer, Farre erred in con- 
