Embryonic development of the wings 126 Evagination of the wing outside of the body 132 Extension of the wing; drawing out of the tracheoles 133 _f._ The primitive origin of the wings 137 The development and structure of the tracheæ and veins of the wing 144 _g._ Mechanism of flight 148 Theory of insect flight 150 Graber’s views as to the mechanism of the wings, flight, etc. 153 THE ABDOMEN AND ITS APPENDAGES 162 The median segment 163 The cercopoda 164 The ovipositor and sting 167 The styles and genital claspers (Rhabdopoda) 176 Velum penis 181 The suranal plate 181 The podical plates or paranal lobes 182 The infra-anal lobe 183 The egg-guide 183 THE ARMATURE OF INSECTS: SETÆ, HAIRS, SCALES, TUBERCLES, ETC. 187 The cuticula 187 Setæ 188 Glandular hairs and spines 190 Scales 193 Development of the scales 195 Spinules, hair-scales, hair-fields, and androconia 197 THE COLORS OF INSECTS 201 Optical colors 201 Natural colors 203 Chemical and physical nature of the pigment 206 Ontogenetic and phylogenetic development of colors 207 2. INTERNAL ANATOMY THE MUSCULAR SYSTEM 211 Musculature of a caterpillar 213 Musculature of a beetle 213 Minute structure of the muscles 215 Muscular power of insects 217 THE NERVOUS SYSTEM 222 _a._ The nervous system as a whole 222 _b._ The brain 226