LIST OF ILLUSTRATIONS.

xiii

FIGURE

26. Shows three of Wolff's cups, each with a central hair, a chitinous ring, and a double ganglionic swelling terminating in a nervefibre, × 500 times. R, R', Sensory pits and hairs; G, G, ganglionic swelling of nerve

PAGE

22

27

27. Under side of left maxilla of Vespa. Gm, Taste-cups; Shm, protecting hairs; Tb, tactile hairs; Mt, base of maxillary palpus 28 28. Section through a taste-cup. SK, Supporting cone; N, nerve; SZ, sense-cell

28

29

29. Tip of the proboscis in the hive bee (Apis), × 140. L, Terminal ladle; Gs, taste-hairs; Sh, guard-hairs; Hb, hooked hairs 30. Organ of taste of fly (Musca vomitoria). gn, Nerve; 99, ganglion; ax, axe-cylinder; gc, terminal cylinder; gk, terminal cone 30 31. Epithelial and (B) olfactory cells of man.. 32. Cells from the olfactory region of a proteus (after Stricker). a, Epithelial cells; b, the apparent processes; c, olfactory cells. A, ciliæ

..

33. Section through the head segment of Polyophthalmus, × 300. Imd, muscle; bo, cup-shaped organ; cu, cuticle; hp, hypoderm; Imd, longitudinal dorsal muscle; n, peripheral nerve; b, cerebral ganglion; cz, commissure of brain; mb, membrane; pmg, pigment cells; hpdz, unicellular glands in the hypoderm; gn, brain; k, nuclei in the brain

34. Antenna of Pontella Bairdii (Lubbock)
35. Terminal segments of one of the smaller antennæ of the water-
woodlouse (Asellus aquaticus), × 500. a, Ordinary hairs (not
connected with a nerve); b, hairs of touch (with a nerve at
the base); c, special cylinders (olfactory cylinders) ..
36. Tip of the antenna of a centipede (Julus terrestris), × 600. At
the apex are four olfactory cylinders, a few of which are also
seen on the following segment, among the ordinary hairs
37. End of a palpus of Staphylinus erythropterus, × 600. a, Olfac-
tory pit

38. Part of antenna of Callianassa subterranea. b, Olfactory hairs;
g, peculiar curved hairs..

39. Terminations of olfactory hairs of Crustacea.

51

42. Section through part of the antenna of a wasp, × 430.

CH,

Chitinous skin; Z, olfactory cone; G, olfactory pit; TB, tac

Palomon; b, of a Pagurus; c, of a Pinnotheres; d, of a Squilla;
e, of a Pontonia

40. Antenna of blowfly. a, Enlarged third segment, showing pits;

xiv

FIGURE

LIST OF ILLUSTRATIONS.

..

PAGE

tile hairs; H, hypodermic cells; M, the membrane surrounding them; K, nuclei of the olfactory cell; K, remains of the earlier upper nucleus; SK, lower circle of rods; RS, olfactory rod; GZ, Geisselzelle; MZ, membrane forming cell; M, membrane closing the pit .. 55 43. Diagram showing structures on the terminal segment of the antennæ of insects. a, Chitinous cuticle; b, hypodermic layer; c, ordinary hair; d, tactile hair; e, cone; f, depressed hair, lying over g, cup, with rudimentary hair at the base; h, simple cup; , champagne-cork-like organ of Forel; k, flask-like organ; 7, papilla, with a rudimentary hair at the apex 44. Leg of Stenobothrus pratorum

45. Sound-bow of Stenobothrus

46. Diagram of human ear. D, Auditory canal; E, mouth of Eustachian tube; cc, tympanic membrane; B, tympanic cavity; o, fenestra ovalis; r, fenestra rotunda; s, semicircular canals; A, cochlea

47. Ossicles of the ear. H, Hammer; Am, anvil; Am. k, shorter process of the anvil; Am. 7, longer process of the anvil; S, stirrup; St, long process of the hammer

48. Section through the ampulla. N, nerve; z, terminal cells; h,
auditory hairs
49. Tympanal wall of the ductus cochlearis, from the dog. Surface
view from the side of the scala vestibuli, after the removal of
Reissner's membrane, 300. I. Zona denticulata Corti. II. Zona
pectinata Todd-Bowman: 1, Habenula sulcata Corti; 2, Ha-
benula denticulata Corti; 3, Habenula perforata Kölliker.
III. Organ of Corti: a, portion of the lamina spiralis ossea
(the epithelium is wanting); b and c, periosteal blood-vessels;
d, line of attachment of Reissner's membrane; e and e,, epi-
thelium of the crista spiralis; f, auditory teeth, with the
interdental furrows; g, g,, large-celled (swollen) epithelium
of the sulcus spiralis internus, over a certain extent shining
through the auditory teeth; from the left side of the pre-
paration they have been removed; h, smaller epithelial cells
near the inner slope of the organ of Corti; k, openings through
which the nerves pass; i, inner hair cells; 7, inner pillars;
m, their heads; o, outer pillars; n, their heads; p, lamina
recticularis; q, a few mutilated outer hair cells; r, outer
epithelium of the ductus cochlearis (Claudius's cells of the
author's); removed at s in order to show the points of attach-
ment of the outer hair cells

62

78

78

79

80

LIST OF ILLUSTRATIONS.

XV

FIGURE

50. Eutima gigas

51. Auditory organ of Ontorchis Gegenbauri
52. Auditory organ of Phialidium. d', Epithelium of the upper
surface of the velum; d2, 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
53. Auditory organ of Rhopalonema, still showing a small orifice.
kk, Modified tentacle; o, auditory organ

..

PAGE

83

84

85

85

86

54. Sense-organ of Pelagia. o, Group of crystals, sk, sense-organ; sf, fold of the skin; ga, gastro-vascular channel

55. Auditory organ of Unio. a, Nerve; b, cells; c, ciliæ; d, otolithe 56. Auditory organ of Pterotrachea Friderici. Na, Auditory nerve; c, central cells; d, supporting plate; b, outer circle of auditory cells; a, ciliated cells

rinus).

57. Base of right antennule of lobster (Astacus marinus). a, Orifice;
S, sac
58. Interior of auditory sac of lobster. a, Orifice; h, auditory hairs
59. Part of wall of auditory sac of lobster (Astacus marinus). a,

Thickened bars in the membrane of the sac; n, first row of
auditory hairs; n', second row of auditory hairs; n", third row
of auditory hairs; n'", fourth row of auditory hairs ; e, grains
of sand, serving as otolithes
60. Auditory hair of crab (Carcinus mænus), × 500. a, Skin; c,
nerve; h, delicate intermediary membrane or hinge..

62. Tail of Mysis vulgaris, showing the auditory organ
63. Part of the leg of a grasshopper (Gryllus). o, t, n, b, tympanum
64. Section through the tibia (leg) of a Meconema, × about 150.

tr, tr, The two trachea; ar, the auditory rod

65. The trachea and nerve-end organs from the tibia (leg) of a
grasshopper (Ephippigera 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; Gr,
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 ..
66. Auditory rod of a grasshopper (Gryllus viridissimus). fď,
Auditory rod; ko, terminal piece

858

87

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

b

xvi

LIST OF ILLUSTRATIONS.

FIGURE

hopper (Meconema). c, Cuticle; a.r, auditory rod; a.c,
auditory cell; tr, trachea

PAGE

105

68. Outer part of a section through the tibia of a Gryllus viridissimus. h, Hard surface of leg; tr, trachea; F, fat bodies; Su, suspensor of the trachea; v W, tracheal wall; TN, nerve; gz, ganglionic cells; rb, tissue connecting the ganglionic cells; E. Sch., end tubes of the ganglionic cells, each containing an auditory rod; fa, terminal threads of ditto

69. Tibia of yellow ant (Lasius flavus), × 75. S, S, Swellings of large trachea; rt, small branch of trachea; a, auditory organ 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

72. Right half of eighth segment of the body of the larva of a gnat
(Corethra plumicornis). EG, Ganglia; N, 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; Im, longitudinal
muscle

73. Head of a gnat

74. Diagram showing one possible mode of vision

106

107

109

110

114

119

120

75. Diagram showing a second possible mode of vision
76. Diagram showing a third possible mode of vision
77. Diagram of human eye. G, Vitreous humor; L, lens; W,

aqueous humor; c, ciliary process; d, optic nerve; e e, sus-
pensory ligament; k k, hyaloid membrane; ƒ ƒ, h h, cornea;
g, choroid; i, retina; 7, ciliary muscle; mf, nf, sclerotic coat;
pp, iris; s, the yellow spot.

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..

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. × 800

80. Diagram to prove the existence of the blind spot in the eye 81. Pineal eye-scale on the head of a small lizard (Calotis)

LIST OF ILLUSTRATIONS.

xvii

FIGURE

82. Diagram of a section through the skull and pineal eye of Lacerta viridis. C, Cuticle; Pa, parietal bone; Ep, epidermis; L, lens; Pig, Pigment; R, rete mucosum; CH, cerebral hemisphere; N, nerve; Ep, epiphysis; OpL, optic lobe of brain

84. Section through the simple eye of a young Dytiscus larva. 7, Corneal lens; g, cells forming the vitreous humor; r, retina; o, optic nerve; h, hypoderm

85. Eye-spot of Lizzia. oc, Ocellus; 7, lens

86. Eye-bulb of Astropecten

87. Eye of Asteracanthion. c, Cuticle; e, epithelium; 7, lens; p, pigment ..

88. Anterior extremity of a freshwater worm (Bohemilla comata). a, Eye; b, brain; c, cuticle; hp, hypoderm; lb, tactile hair; ne, nerve; v, blood-vessel

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128

130

131

132

132

133

135

135

89. Eye-dot of Nereis. In B the pigment is partly removed so as
to show the lens
90. The first twelve segments of Polyophthalmus pictus, seen from
below. The Roman numerals indicate the segments. St,
Papillæ on the head; KS, head; au, head eye; s.au, side eyes;
Ol, upper lip; Ul, under lip; v.ph, pharyngeal vein; V.subinta,
anterior ventral vein; V.d.l1-, veins connecting the superior
lateral and vessels; sept1-3, intersegmentary membranes;
m.ocs.l, lateral muscle of the oesophagus; V.ann, pulsating
circular vessel; Md.dr, stomach-glands; V.v-l, vein con-
necting the inferior and lateral blood-vessels; Md, stomach;
Bm, muscles of the hairs; G, brain; fl.o, ciliated organ; qm,
transverse muscle

91. Alciope

136

137

92. Perpendicular section through the eye-pit of a limpet (Patella). 1, Epithelial cells; 2, retina cells; 3, vitreous body

138

138

139

93. Eye of Trochus magus. Gl, Vitreous body; No, nerve
94. Eye of Murex brandaris. L, Lens; Gl, vitreous body; No, nerve
95. Eye of Helix pomatia. ct, Cuticle; a, epithelium; b, cornea;
c, envelope of the eye; d, cellular layer; e, fibrils of the optic
nerve; f, feeler cell; na, nerve of the tentacle; no, optic

96. Perpendicular section through an eye of Arca noœ. 1, Epithe-
lium of the edge of the mantle; 2, cells of vision; 3, lens;
4, 5, connective tissue; 6, section of one of the cells
97. Diagram of eye of Pecten. a, Cornea; b, transparent basement
membrane supporting the epithelial cells of cornea; c, the