TABLE OF CONTENTS XV 



5. THE CIRCULATORY SYSTEM 121 



The general features of the circulatory system 121 



The heart 121 



The pulsations of the heart 122 



The aorta 122 



The circulation of the blood 122 



Accessory circulatory organs 122 



6. THE BLOOD 122 



7. THE ADIPOSE TISSUE I23 



8. THE NERVOUS SYSTEM I23 



a. The central nervous system 123 



b. The oesophageal sympathetic nervous system 125 



c. The ventral sympathetic nervous system 127 



d. The peripheral sensory nervous system 128 



9. GENERALIZATIONS REGARDING THE SENSE-ORGANS OF INSECTS.. . I29 



A classification of the sense-organs 129 



The cuticular part of the sense-organs 130 



XO. THE ORGANS OF TOUCH I3I 



11. THE ORGANS OF TASTE AND SMELL I32 



12. THE ORGANS OF SIGHT I34 



a. The general features 134 



The two types of eyes 134 



The distinction between ocelli and compound eyes 134 



The absence of compound eyes in most of the Apterygota 135 



The absence of compound eyes in larvae 135 



b. The ocelli I35 



The primary ocelli I35 



The adaptive ocelli 136 



The structure of a visual cell i37 



The structure of a primary ocellus I37 



Ocelli of Ephemerida I39 



c. The compound eyes I39 



The physiology of compound eyes 141 



The theory of mosaic vision 141 



Day-eyes 142 



Night-eyes ^43 



Eyes with double function I43 



Divided eyes ^44 



The tapetum ^44 



