SLIME SLUGS, MYRIAPODS AND INSECTS 135 



feet, for it is on the claws and little pads present on these seg- 

 ments that the insect stands. Insects that can climb on 

 smooth surfaces or walk on overhanging walls have small 

 hollow hairs on the pads of the feet from which a sticky se- 

 cretion issues. 



Wings. Bees' wings are four in number, which is the typical 

 number for insects in general. However, many insects, in- 

 cluding all the true flies or Diptera, have but a single pair of 

 wings. Parasitic insects, such as fleas, lice, etc., are usually 

 wingless. All of the living wingless insects, except a single 

 small grsup called the Aptera, are believed to have lost their 

 wings by degeneration. The Aptera, however, are believed 

 to be the immediate descendants of the primitive wingless 

 ancestors of the whole great insect class. 



The bees' wings are membranous, very thin and trans- 

 parent, and supported on a framework of branching veins. 

 The wings of many insects, however, are thickened, as for ex- 

 ample the fore wings of grasshoppers and all beetles. The wing 

 veins may be few in number as with the bee and house-fly, 

 or many, as in the hind wings of the grasshoppers. Most 

 of the butterflies and moths have their wings covered com- 

 pletely above and below with fine scales in which pigment of 

 various colors is held. In the two-winged flies it is the hind- 

 most pair of wings that is lost, or rather is replaced by a pair 

 of very different structures, small stems with expanded tips, 

 called balancers. In one small group of insects, however, it 

 is the front pair of wings that is gone. 



The two wings on each side of the bee's body can be fastened 

 together, and are, when the bee is flying, by a row of tiny 

 hooks along the front margin of the hind wing which catch 

 hold of the hind margin of the front wing. This is a device 

 which makes the bee practically two-winged when in flight. 

 Some other insects, as most of the butterflies and moths, 

 for example, also have means for fastening the two wings of 

 each side together. 



Sting. The appendages of the abdomen, although several 

 in number, are all combined to form the sting. This sting 

 is made up of a sheath containing two movable barbed darts 



