INTRODUCTION. © 
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It will be necessary to look at Fig. 13 in order to see the organs 
of respiration of which we are speaking. 
The respiratory mechanism of an insect is easily understood. 

























Fig. 13.—A, abdominal portion of the dorsal vessel. B, aortic or thoracic portion. C, air-vessels of the 
head; D, of the abdomen. 
“The abdominal cavity,” says M. Milne Edwards, “in which is 
placed the greater part of the respiratory apparatus, is susceptible 
C 
