xiv TABLE OF CONTENTS 



b. The fore-intestine 109 



The layers of the fore-intestine 1 09 



The intima 109 



The epithelium 1 09 



The basement membrane 109 



The longitudinal muscles 109 



The circiilar muscles 1 09 



The peritoneal membrane 109 



The regions of the fore-intestine 109 



The pharynx 109 



The oesophagus no 



The crop no 



The proventriculus no 



The oesophageal valve in 



c. The mid-intestine in 



The layers of the mid-intestine 1 1 1 



The epithelium 112 



The peritrophic membrane 112 



d. The hind-intestine 112 



The layers of the hind-intestine 112 



The regions of the hind-intestine 113 



The Malpighian vessels 113 



The Malpighian vessels as silk-glands 113 



The caecum 113 



The anus 113 



4. THE RESPIRATORY SYSTEM 113 



a. The open or holopneustic type of respiraotry organs 114 



1. The spiracles 114 



The position of the spiracles 114 



The number of spiracles 114 



Terms indicating the distribution of the spiracles 115 



The structure of spiracles 1 16 



The closing apparatus of the tracheae 1 16 



2. Tine trachea; 116 



The structure of the tracheae 117 



3 . The tracheoles 118 



4. The air-sacs 1 1 8 



5. Modifications of the open type of respiratory organs 119 



b. The closed or apneustic type of respiratory organs 119 



/. The Tracheal gills 1 19 



2. Respiration of parasites 120 



j. The blood-gills 120 



