2OO 



THE BOOK OF NATURE STUDY 



substance by which the animal can adhere to smooth vertical 

 or even inverted surfaces. 



In addition to their locomotor function, the legs have the 

 important duty of keeping the body clean and free from particles 

 of dust and other foreign objects. A wasp or any other insect 

 may often be seen to pass its legs over various portions of the 

 body, and then rub the legs so used together, or between two 

 others, or pass them between the mandibles. The first procedure 

 is in order to entangle the dust lying on the body in the bristles 

 which cover the tibia, and especially the tarsus, 

 the second is to remove the matter so collected and 

 drop it to the ground. The bristles which cover the 

 legs all point away from the body and towards the 

 claws, and thus tend to work the dust particles 

 off and not on to the body. Those upon the 

 ventral side of the tarsal joints are worth detailed 

 description : between the two claws are two stout 

 bristles starting from the dorsal side of the ad- 

 hesive pad, but reaching to the ground in front of 

 it ; behind the pad on the ventral side are four 

 similar bristles, two on each side, lying straight 

 behind the claws and nearer to the margins than 

 the two dorsal bristles ; the fourth tarsal joint 

 carries four such bristles upon each side, the third 

 five, the second six, the first (a long joint often 

 metatarsus ") seven. Now, since the transverse 

 width of these several joints is approximately the same, it follows 

 that in passing from the fifth to the first joint one en- 

 counters a succession of combs or rakes whose teeth become 

 gradually more and more closely set. Hence, when the leg 

 is used as a cleanser, a coarse rake goes over the surface first, 

 and is followed by four other rakes of increasing fineness, so 

 that the larger particles of dust are first removed and then the 

 more minute. In addition to these stout bristles there are 

 many very fine ones, which cover the edges and ventral surface of 

 all the tarsal joints ; while the metatarsus has, beyond those 

 already mentioned, some five-and-twenty coarse bristles along 

 the length of its under side, and a similar arrangement occurs 



FIG. 72. 

 called the 



