INTRODUCTION. 



17 



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 thoraic portion. C, air-vessels of the 

 head ; D, of the abdomen. 



" The abdominal cavity/' says Mr. Milne Edwards, " in which is 

 placed the greater part of the respiratory apparatus, is susceptible 



c 



