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) 38. Part of antenna of Callianassa subterranea. b, Olfactory 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; 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, 62 78 78 79 80 LIST OF ILLUSTRATIONS. XV FIGURE 50. Eutima gigas 51. Auditory organ of Ontorchis Gegenbauri .. 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; Thickened bars in the membrane of the sac; n, first row of 62. Tail of Mysis vulgaris, showing the auditory organ tr, tr, The two trachea; ar, the auditory rod 65. The trachea and nerve-end organs from the tibia (leg) of a 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, 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 h, simple hair; tg, ganglion of tactile hair; Im, longitudinal 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 aqueous humor; c, ciliary process; d, optic nerve; e e, sus- 78. Section through the retina. 1, Limitary membrane; 2, layer 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 PAGE 128 130 131 132 132 133 135 135 89. Eye-dot of Nereis. In B the pigment is partly removed so as 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 96. Perpendicular section through an eye of Arca noœ. 1, Epithe- |