Vlll CONTENTS. 



CHAPTER IV. 



PAGE 



The sense of hearing — Organs of sound — Mullusca — Crustacea — 

 Insects — Locusts — Grasshoppers — Crickets — Cicadas — 

 Beetles — The bombardier beetle — Paussus — Death-watch — 

 Burying beetles — Weevils — Cockchafers — Variety of organs 

 of sound among beetles— Diptera — Hymenoptera— Ants — 

 Bees— Sounds produced in flight— Power of varying sound 

 — Butterflies — Moths — Centipedes — Spiders — Power of hear- 

 ing in Insects— Sense of hearing in insects ... ... 60 



CHAPTER V. 



The organs of hearing — Structure of the human ear — The organ 

 of Corti — Mode of action of auditory organs— Organs of 

 hearing in the lower animals — Medusae — Auditory hairs — 

 Mollusca — Annelides — Crustacea — Use of grains of sand as 

 otolithes — Ear in tail of Mysis— Mode of hearing— Organs 

 of hearing in insects — Seat of the sense of hearing in insects 

 — Difierent seats of organs of sense — Ears in legs of crickets 

 — Ear of grasshoppers — Structure of ear — Auditory rods — 

 Ear of locusts— Peculiar structure in leg of ant — Origin of 

 ear — Ear of fly — Peculiar sense-organs— Auditory rods in 

 beetles — Position of auditory rods — Chordotonal organs — 

 Auditory hairs of antennae of gnat — Sympathetic vibrations 

 — Organs of hearing in various parts of body ... ... 77 



CHAPTER VI. 



The sense of sight — Three possible modes of sight— Difierent 

 forms of eye— The vertebrate eye— Structure of the eye— 

 The retina— The rods and cones — The blind spot in the eye 

 —Inversion of the rods — The pineal gland— The rudimentary 

 median eye — The median vertebrate eye — The organs of 

 vision in the lower animals— Color-spots — Echinoderms — 

 Worms— Molluscs— Cuttle-fish— Compound eyes in Molluscs 

 —Area— Spondylus—Pecten—Onchidium— Sense-organs of 

 Chiton 118 



CHAPTER VII. 



The organs of vision in Insects and Crustacea— Ocelli— Compound 

 eyes — Cornea— Crystalline cones — Retinula — Pigment — 

 Different forms of eyes— Structure of the optic lobes— Eyes 



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