232 



. THE RISE OF ANIMAL LIFE 



ocelli 



antennoe. 



labrum 



moxilia 



antennae 

 enlarged 



sensory 

 plate 



sensory hair 



Fig. 11-27. The head of the bee, showing the mouth parts. An antenna has been enlarged in cross-section to show 



the details of the sensory end organs. 



gum) is forced upward. This pulls the dor- 

 sal basal edge of the wing upward, causing 

 the wing as a whole to be forced downward 

 with considerable force; the body wall acts 

 as a fulcrum. The upstroke is accomplished 

 by the sudden contraction of the dorsal- 

 ventral muscles in a similar manner. Thus 

 the wings move up and down by the throb- 

 bing of the thorax and not by any effort on 

 the part of the wing itself. Its pitch can be 

 altered so that the bee can hover, fly for- 

 ward, or fly backward with ease, something 

 man has had great difficulty in duplicating 

 mechanically. In the heHcopter this has 

 been accomplished to a certain degree. 

 Bees are capable of long flights, sometimes 

 as long as 10 miles, although usually much 

 shorter distances are covered in their rou- 

 tine work. 



Another interesting modification of the 

 bee's appendages is the sting. This is found 

 only in the females, workers and queen, be- 

 cause it is homologous to the ovipositor. The 

 organ has become a complicated apparatus, 

 retaining the muscle system which made it 

 possible for the grasshopper to deposit its 

 eggs in very hard soil. In the sting these 

 muscles enable the bee to force sharp- 

 grooved darts into the tough skin of an 

 intruder. A pair of feelers on either side of 

 the darts "selects" the spot where the sting 

 is to be released. This prevents the bee 

 from stinging inert bodies. Lying between 

 the upper ends of the darts is the poison sac 

 which is in contact by means of ducts with 

 an alkaline and an acid gland. During 

 the stinging procedure the poison sac is 

 squeezed, and its product is forced into the 



