longitudinal muscles' 

 vertical muscles 



ANIMALS WITH JOINTED FEET-THE ARTHROPODS 



The external surface of the bee is cov- 

 ered with "hairs." Those over the eyes are 

 straight and unbranched, whereas those 

 over the remainder of the body are 

 branched, thus affording a place for pollen 

 to cling. During a visit to a flower, the bee 

 gathers some pollen with its mandibles and 

 moistens it with honey. Pollen is also ob- 

 tained from the action of the pollen brushes 

 on the front two pairs of legs which clean 

 the anterior portion of the body (Fig. 

 11-25). These brushes pass the sticky pollen 

 mass back to the middle legs which rub 

 it upon the pollen combs of the hind legs. 

 The pollen is then rubbed from the right 

 hind leg onto the left and from the left onto 

 the right, and thus carried to the pollen 

 packer, which is composed of two parts, the 

 auricle and the pecten. Once the pollen has 

 reached this position, the tarsus is flexed 

 on the tibia, packing the pollen from the 

 bottom into the pollen basket (Fig. 11-25), 

 A great quantity of pollen may be collected 

 in this way so that when the bees fly home 

 in the late afternoon the huge balls of pol- 

 len cause the hind legs to dangle much 

 lower than when they are not so loaded. 



The anterior pair of legs has two cleaning 

 mechanisms, an eye brush and an antenna 

 cleaner, which the bee uses to remove pol- 

 len from these organs. The antenna cleaner 

 is composed of a velum, a small flexible 

 projection from the tibia, and a crescent- 

 shaped depression on the proximal end of 

 the tarsus, lined with short bristles. The 

 antenna is brought into this depression and 

 pulled through several times to clean it. In 

 addition to the pollen brush on the middle 

 pair of legs, there is also a spur, which is 

 used in picking and transferring wax in the 

 process of comb-building. 



The bee has two pairs of delicate mem- 

 branous wings which can operate either 

 separately or locked together by means of 

 a row of hooks that fasten into a groove in 

 the posterior margin of the forewing (Fig. 

 11-25). During a straight flight, where 

 speed is essential, the wings are locked to- 



231 



wing process 



Fig. 11-26. Cross-section of the bee showing how the 

 wings function ciuring flight. 



gether and the bee flies as if it had only 

 two wings. The question of flight in insects 

 has been a puzzling one, not only to biolo- 

 gists but to engineers as well. The latter 

 claim that, according to aerodynamics, a 

 bee cannot fly! Aside from speed, flight in 

 insects exceeds anything the engineer has 

 been able to devise so far, yet aircraft de- 

 signers have so far been unable to apply the 

 principle employed by these little animals. 

 Flight in insects is brought about in a pe- 

 culiar manner, namely, not by wing mus- 

 cles, as in the case of birds, but by powerful 

 muscles which cause the thorax to vibrate 

 and this in turn forces the wings to flap up 

 and down. In Fig. 11-26 this is illustrated. 

 As the anterior-posterior thoracic muscles 

 contract, the dorsal wall of the thorax (ter- 



