The optic or procerebral segment 231 Procerebral lobes 232 The mushroom or stalked bodies 233 Structure of the mushroom bodies 234 The central body 237 The antennal or olfactory lobes (Deutocerebrum) 237 The œsophageal lobes (Tritocerebrum) 237 _c._ Histological elements of the brain 238 _d._ The visceral (sympathetic or stomatogastric) system 238 _e._ The supraspinal cord 240 _f._ Modifications of the brain in different orders of insects 240 _g._ Functions of the nerve-centres and nerves 243 THE SENSORY ORGANS 249 _a._ The eyes and insect vision 249 The simple or single-lensed eye (ocellus) 249 The compound or facetted eye (ommateum) 250 The facet or cornea 250 The crystalline lens or cone 251 The pigment 253 The basilar membrane 253 The optic tract 253 Origin of the facetted eye 255 Mode of vision by single eyes or ocelli 255 Mode of vision by facetted eyes 256 The principal use of the facetted eye to perceive the movements of animals 259 How far can insects see? 260 Relation of sight to the color of eyes 260 The color sense of insects 260 _b._ The organs of smell 264 Historical sketch of our knowledge of the organs of smell 264 Physiological experiments 268 Relation of insects to smelling substances before and after the loss of their antennæ 269 Experiments on the use of the antennæ in seeking for food 270 Experiments testing the influence of the antennæ of the males in seeking the females 270 Structure of the organs of smell in insects 271 _c._ The organs of taste 281