PL IX. — I. Wing-pad of mayfly nymph; dark lines are 

 the tracheas; soft gray lines represent the developing veins. 

 2. Air-tubes or tracheae of a dragonfly nymph in dorsal 

 view; the alimentary canal lies between the two large 

 tracheae but is hidden by masses of fat: a, large trachea (con- 

 nected with spiracles in adult); b, fat; c, tracheae in wall of 

 intestine. 



