170 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



Tlie first good description of the organ, accompanied by figures, was 

 given by the EngUshmau Farre ('43), who carefully dissected the 

 otocysts of the crayfish (Astacus fluviatalis), the European lobster 

 (Astacus mariuus), 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 antennae (autennules), 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 antenuule, 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 irregular!}'' 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, '48), 

 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 fouud in 

 the endopod of the last abdominal appendages of Mysis, mentioning 

 the otolith and auditory hairs. 



Leuckart ('53) made a comparative stud}' 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- 



