52 
TRANSFORMATIONS OF INSECTS. 
breathe very slowly. The energy and the rapidity of the respi- 
ratory efforts increase during any agitation. An insect may be 
crawling over the leaves, or upon the ground, with very little air 
in its tracheae. Its body is heavy, and it could not fly unless it 
contained more air ; so the insect lifts up its wings, and makes 
a few energetic movements of its abdomen, in order to fill the 
vesicles and tracheae to the utmost, and sails away. 
The long voyages of immense columns of locusts are well 
