LIST OF ILLUSTEATIONS. XV 



FIGUEK PAGE 



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



51. Auditory organ of Ontorchis Gegenbauri . . . . . . 84 



52. Auditory organ of Phialidium. d\ Epithelium of the upper 



surface of the velum; d'^, epithelium of the under surface of 

 the velum ; hh, auditory hairs ; h, auditory cells ; 7ip, 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. o, Group of crystals , sk, sense-organ ; 



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



55. Auditory organ of Unio. a, Nerve ; b, cells ; c, ciliiie ; d, otolithe 87 



56. Auditory organ of Fterotrachea Friderici. Na, Auditory nerve ; 



c, central cells ; d, supporting plate ; 6, 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 ; A, auditory hairs 88 



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



Thickened bars in the membrane of the sac; tj, first row of 

 auditory hairs ; 77', second row of auditory hairs ; 7]", third row 

 of auditory hairs ; 7)'", fourth row of auditory hairs ; e, grains 

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



60. Auditory hair of crab (^Carcinus mccnus), X 500. a, Skin ; c, 



nerve ; A, 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). 0, t, n, b, tympanum 98 



64. Section through the tibia (leg) of a Meconema, 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 (^Ephippigera vitium). EBI, Terminal vesicles of 

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

 the trachea ; hTr, hinder branch of the trachea ; /S'iV", nerves 

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

 group of vesicles of the organ of Siebold ; vJSf, 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 ; ko, terminal piece . . . . . . . . 104 



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



h 



