LIST OP ILLUSTEATIONS. xv 



FIGURE PAGE 



50. Eutima gigas . , . . , , . . . . . , , . 83 



51. Auditory organ of OntorcMs Gegenbauri . . . . . . 84 



52. Auditory organ of Phialidium. d', Epithelium of the upper 



surface of the velum; cP, epithelium of the under surface of 

 the velum ; AA, auditory hairs ; A, auditory cells ; np, nervous 

 cushion ; nr', nerve-ring ; r, circular canal at the edge of the 

 velum , . . . . . . . , . . . . . . . 85 



53. Auditory organ of Rhopalonema, still showing a small orifice. 



kk, Modified tentacle ; o, auditory organ . . . . . . 85 



54. Sense-organ of Pelagia. u, Group of crystals , sk, sense-organ ; 



sf, fold of the skin ; ga, gastro-vascular channel . . . . 86 



55. Auditory organ of Unio. a, Nerve ; 6, cells ; c, ciliae ; d, otolithe 87 



56. Auditory organ of Pterotrachea Friderioi, JTa, Auditory nerve ; 



c, central cells; d, supporting plate ; &, outer circle of audi- 

 tory cells ; a, ciliated cells . . . . . . . . . , 87 



57. Base of right antennule of lobster (^Astacus marinus). a, Orifice ; 



s, sac . . . . . . . . . . . . . . . . 88 



58. Interior of auditory sac of lobster, a. Orifice ; h, auditory hairs 88 



59. Part of wall of auditory sac of lobster (Astacus mmnus). a, 



Thickened bars in the membrane of the sac ; t], first row of 

 auditory hairs ; ?)', second row of auditory hairs ; rj", third row 

 of auditory hairs ; i)'", fourth row of auditory hairs ; e, grains 

 of sand, serving as otolithes . . . . . . . . . . 89 



60. Auditory hair of crab (CarareMS mwnus), X 500. a, Skin ; c, 



nerve ; h, delicate intermediary membrane or hinge . . . . 92 



61. Mysis 92 



62. Tail of Mysis vulgaris, showing the auditory organ . . . . 93 



63. Part of the leg of a grasshopper (Gryllus). o, ^, n, 6, tympanum 98 



64. Section through the tibia (leg) of a Meconemn, x about 150. 



tr, tr, The two tracheae ; ar, the auditory rod . . . . 102 



65. The tracheae and nerve-end organs from the tibia (leg) of a 



grasshopper QEp/iippigera vitiuni). JEBI, Terminal vesicles of 

 Siebold's organ ; ST, hinder tympanum ; Sp, space between 

 the trachea ; TiTr, hinder branch of the trachea ; SN, nerves 

 of the organ of Siebold ; go, supra-tympanal ganglion ; Gr, 

 group of vesicles of the organ of Siebold ; siV, connecting 

 nerve-fibrils between the ganglionic cells and the terminal 

 vesicles ; So, nerve terminations of the organ of Siebold ; vT, 

 front tympanum ; vTr, front branch of the trachea . . . , 103 



66. Auditory rod of a grasshopper (^Gryllus viridissimus}. fd', 



Auditory rod ; fo, terminal piece . . . . . , . . 104 



67. Diagram of a section through the auditory organ of a grass- 



