ORGANS OF LOCOMOTION S'OR A PLYING LIFE 307 



of the body walls, and forcing this ejected water through 

 a funnel at the front of the body. 



Organs of locomotion for a flying life. — All animals 

 which fly require special adaptations of structure to 

 lighten the body, and also very powerful muscles to keep 

 the body in motion, while the form of paddle or wing used 

 to push the body through the air must be much broader 

 in proportion to the size than were those used in pushing 

 against the water. 



The bodies of flying insects are lightened by air sacs 

 and cavities distributed through the body, while in birds 

 similar air sacs and hollow light bones serve them for the 

 same purpose. Feathers in the bird are adaptations for 

 a body covering which secure lightness and protection at 

 the same time. 



The wings of insects are expansions of the skin or body 



h 



Fig. 140 Cross section of an insect; h, heart; a, alimentary canal; to, nerve 



ganglia ; t, air tubes (trachea) which carry air to all parts of the body and form 

 the veins of the wings. 



