THE PERIODICAL CICADA 



The head ot the cicada is thus seen to be a wonderful 

 mechanism tor enabling the insect to feed on plant sap. 

 The piercing beak and the sucking apparatus, however, 

 are characters distinguishing the members of a whole 

 order of insects, the Hemiptera, or Rhynchota. This 

 order includes, besides the cicadas, such familiar insects 

 as the plant lice, the scale insects, the squash bugs, 

 the giant water bugs, the water striders, and the bed 

 bugs. To the sucking insects properly belongs the name 

 "bug," which is not a synonym of "insect." 



It is believed, of course, that the parts of the sucking 

 beak of a hemipteran insect correspond with the mouth 

 parts of a biting insect, described in Chapter IV (Fig. 

 66), but it has been a difficult matter to determine the 

 identities of the parts in the two cases. Probably the 

 anterior narrow plate on the side of the cicada's head 

 (Fig. 121, Md) is a rudiment of the base of the true jaw, 

 or mandible. The first bristles (MdB) are outgrowths 

 of the mandibular plates, which have become detached 

 from them and made independently movable by special 

 sets of muscles. The second bristles (MxB) are out- 

 growths of the maxillae, which are otherwise reduced 

 to small lobes (Mx) depending from the cheek plates 

 (Ge). The sheath of the beak (Lb) is the labium. We 

 have here, therefore, a most instructive lesson on the 

 manner in which organs may be made over in form, by 

 the processes of evolution, adapting them to new and 

 often highly special uses. 



The abdomen of the cicada is thick, and strongly 

 arched above. Its external appearance of plumpness 

 suggests that it would furnish a juicy meal for a bird, 

 and birds do destroy large numbers of the insects. Yet 

 when the interior of a cicada is examined (Fig. 123), it is 

 found that almost the entire abdomen is occupied by a 

 great air chamber! The soft viscera are packed into 

 narrow spaces about the air chamber, the stomach (Stom) 

 being crowded forward into the rear part of the thorax. 



[ 205 ] 



