INSECTS 



debris. The insects themselves will give an answer to 

 the question if several of them are placed in glass tubes 

 and covered with earth; but, to understand the cicada's 

 technique, we must first study the mechanism of its 

 digging tools, the front legs. 



The front leg of a mature cicada nymph (Fig. 116 A) is 



composed of the same 

 parts as any other of its 

 legs. The third segment 

 from the base, which is 

 the femur (F), is large 

 and swollen, and has a 

 pair of strong spines and 

 a comb of smaller ones 

 projecting from its lower 

 edge. The next segment 

 is the tibia {Tb). It is 

 curved and terminates 

 in a strong recurved 

 point (B). Finally, at- 

 tached to the inner sur- 

 face of the tibia, well up 

 from its terminal point, 

 is the slender tarsus 

 {Tar). The tarsus can 

 be extended beyond the 

 tibial point when the insect is walking or climbing, but 

 can also be turned inward at a right angle to the latter, 

 as shown at B, or bent back against the inner surface of 

 the tibia. 



Let us now return to the insects in the earth-filled 

 tubes, where they are industriously at work. It will be 

 seen that they are using the curved, sharp-pointed tibiae 

 as picks with which to loosen the earth, the tarsi being 

 turned back and out of the way. The two legs, working 

 alternately, soon accumulate a small mass of loosened 

 material in front of the insect's body. Now there is a 



[ 19°] 



Fig. 116. The digging organ, or front 



leg, of the mature cicada nymph 

 A, right leg, inner surface (4 times natural 

 size). B, the tarsus {Tar) bent inward at 

 right angles to the tibia (7^), the posi- 

 tion in which it is used as a rake 

 Cx, basal joint or coxa; Xr, trochanter; F } 

 femur; Tb, tibia; Tar, tarsus, with two 

 terminal claws 



