LIST OF ILLUSTRATIONS. XV 



FIGURE PAGE 



50. Eiitima gigas . . . , , . . . . . . . . . 83 



51. Auditory organ of Ontorchis Gege)vbauri . . . . . . 84 



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



surface of the velum; c?-, epithelium of the under surface of 

 the velum ; hh, auditory hairs ; h, auditory cells ; np, nervous 

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

 velum . . . . . . . . . . . . . . . . 85 



53. Auditory organ of P.hopalonema, 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 ; 6, cells ; c, cilit? ; d, otolithe 87 



56. Auditory organ of Pterot-rachea 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 (J.s^acMsmarmws). a, Orifice ; 



s, sac . . . . . . . . . . . . . . . . ttS 



58. Interior of auditory sac of lobster, a, Oi'ifice ; h, auditory hairs 88 



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



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

 auditory hairs ; tj', second row of auditory hairs ; t]", third row 

 of auditory hairs ; tj'", fourth row of auditory hairs ; e, grains 

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



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



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



61. Mysis 92 



62. Tail of Ilysis vulgaris^ showing the auditory organ . . . . 93 



63. Part of the leg of a grasshopper (Gryllus). o, 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 (^Ephipingera vitium). EBI, Terminal vesicles of 

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

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

 of the organ of Siebold ; go, supra-tympanal ganglion ; (?r, 

 group of vesicles of the organ of Siebold ; vN, 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- 



1) 



