INTRODUCTION, , 17 
It will be necessary to look at Fig. 13 in order to see the oreans 
d ro) DoD 
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. 
¥ 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 
C, air-vessels of the 

