TABLE OF CONTENTS XV 



5. THE CIRCULATORY SYSTEM 121 



The general features of the circulatory system 12 1 



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 123 



The central nervous system 123 



The oesophageal sympathetic nervous system 125 



The ventral sympathetic nervous system 127 



The peripheral sensory nervous system 128 



9. GENERALIZATIONS REGARDING THE SENSE-ORGANS OF INSECTS.. . 1 29 



A classification of the sense-organs 129 



The cuticular part of the sense-organs 130 



10. THE ORGANS OF TOUCH I3I 



11. THE ORGANS OF TASTE AND SMELL I32 



12. THE ORGANS OF SIGHT 134 



The general features I34 



The two types of eyes I34 



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 I35 



The ocelH 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 



The compound eyes I39 



The physiology of compound eyes 141 



The theory of mosaic vision 14^ 



Day-eyes 14^ 



Night-eyes H3 



Eyes with double function i43 



Divided eyes H4 



The tapetum ^44 



