Xvi LIST OF ILLUSTEATIONS. 



FIGURE PAGE 



hopper (Meconema). c, Cuticle ; a.r, auditory rod ; a.o, 

 auditory cell ; ir, trachea . . . . . . • • • • -^"^ 



68. Outer part of a section through the tibia of a Gryllus viri- 



dissimus. h, Hard surface of leg ; tr, trachea; F, fat bodies; 

 Su, suspensor of the trachea ; v W, tracheal wall ; TJf, nerve ; 

 gz, ganglionic cells ; rb, tissue connecting the ganglionic cells ; 

 E. Sch., end tubes of the ganglionic cells, eacli containing an 

 auditory rod ; fa, terminal threads of ditto . . . . . . 106 



69. Tibia of yellow ant {Lasius fiavus), X 75. S, S, Swellings of 



large trachea; rt, small branch of trachea ; a, auditory organ 107 



70. Part of the tibia of Isopteryx apicalis. Sc, Auditory organ ; 



ef, terminal filament; Cu, cuticle; G, ganglionic cell; Sc, 

 structure enclosing the auditory rod ; tr, trachea ; n, nerve 109 



71. One of the halteres of a fly 110 



72. Right half of eighth segment of the body of the larva of a gn.it 



{Corethra plumkornis). EG, Ganglia ; If, nerve ; g, auditory 

 ganglion ; gb, auditory ligament ; Ch, auditory rods ; a, audi- 

 tory nerve ; e, attachment of auditory ligament to the skin ; 

 hn, hn', termination of skin-nerve ; tb, plumose tactile hair; 

 h, simple hair ; tg, ganglion of tactile hair ; hn, longitudinal 

 muscle .. .. .. .. .. .. .. .. 114 



73. Head of a gnat 115 



74. Diagram showing one possible mode of vision .. ., .. 119 



75. Diagram showing a second possible mode of vision ., .. 119 



76. Diagram showing a third possible mode of vision , , . . 120 



77. Diagram of human eye. G, Vitreous humor ; L, lens ; W, 



aqueous humor; c, ciliary process; d, optic nerve; e e, sus- 

 pensory ligament ; A k, hyaloid membrane ', f f, h h, cornea ; 

 g, choroid ; i, retina ; /, ciliary muscle ; mf, nf, sclerotic coat ; 

 ^p, iris; s, the yellow spot. .. .. .. .. .. 121 



78. Section through the retina. 1, Limitary membrane ; 2, layer 



of nerve-fibres ; 3, layer of nerve-cells ; 4, nuclear layer; 5, 

 inner nuclear layer ; 6, intermediate nuclear layer ; 7, outer 

 nuclear layer ; 8, posterior membrane ; 9, layer of small rods 

 and cones ; 10, choroid . . . . . . . . . . . . 123 



79. A, Inner segments of rods (s, s, s) and cones (z, z') from man, 



the latter in connection with the cone-granules and fibres as 

 far as the external molecular layer, 6. In the interior of 

 the inner segment of both rod and cone fibrillar structure is 

 visible. X 800 124. 



80. Diagram to prove the existence of the blind spot in the eye . . 125 



81. Pineal eye-scale on the head of a small lizard (Calotis) .. 127 



