The Life Processes of the Individual 



155 



attachment of the bee's wings to the thorax has been in- 

 vestigated by Snodgrass (I.e. pp. 61-63). 



The motion of the wings in flight is in four directions, up, 

 down, forward and backward, and the combination of thesa 

 movements causes the wing tips to describe the course of a 

 figure 8, if the insect is held stationary. In flight, the 8 

 is of course modified. The hind wings are small and are 

 attached by hooks on their anterior margins to thickenings 

 on the margin of the front wings. They are not provided 

 with large flight muscles of their own but are carried along 

 by the action of the powerful muscles in the mesothorax 

 which propel the fore 

 wings. 



The muscles of flight 

 are in four sets, cor- 

 responding to the four 

 directions of wing move- 

 ment. The chief muscles 

 are not attached directly 

 to the bases of the wings, 



as in dragonflies, but the FIG. 80. Fore and hind wings. 



wings are moved into 



the right position by muscles situated inside the pleura of 

 the two thoracic segments. After the wings are in position 

 for flight, the compression of the thorax by the vertical 

 muscles lowers the dorsum and raises the wing while the 

 contraction of the longitudinal muscles raises the dorsum 

 and lowers the wing. The vertical muscles are therefore 

 the elevators and the longitudinal muscles the [depressors. 

 The movements of the wings during flight is therefore 

 produced mainly by changes in the shape of the thorax. 

 The forward and backward movements are accomplished 

 by the action of the muscles on the pleurum, acting directly 

 on the bases of the wings. 



Because of the enormous development of the two main 

 sets of flight muscles, bees are capable of strong and rapid 

 flight. They are also capable of arresting progress suddenly 



