The labrum 42 The epipharynx and labrum-epipharynx 43 Attachment of the head to the trunk 46 The basal or gular region of the head 46 The occiput 48 The tentorium 49 Number of segments in the head 50 The composition of the head in the Hymenoptera 55 _b._ Appendages of the head 57 The antennæ 57 The mandibles 59 The first maxillæ 62 The second maxillæ 68 The hypopharynx 70 Does the hypopharynx represent a distinct segment? 82 THE THORAX AND ITS APPENDAGES 86 _a._ The thorax: its external anatomy 86 The patagia 89 The tegulæ 89 The apodemes 92 The acetabula 94 _b._ The legs: their structure and functions 95 Tenent hairs 99 Why do insects have but six legs? 100 Loss of limbs by disuse 101 _c._ Locomotion (walking, climbing, and swimming) 103 Mechanics of walking 103 Locomotion on smooth surfaces 111 Climbing 116 The mode of swimming of insects 116 _d._ The wings and their structure 120 The veins 121 The squamæ 123 The halteres 124 The thyridium 124 The tegmina and hemelytra 124 The elytra 124 _e._ Development and mode of origin of the wings 126