CONTENTS. 



CHAPTER IV. 



The sense of hearing — Organs of sound — Mollusca — 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 — Anuelides — 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 

 — Different 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 — Different 

 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 



