PERIODICAL CICA1)A
The head of the cicada is thus seen to be a wonder(ul mechanism for 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 Rhvnchota. 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. "Fo the sucking insects properly belongs the name "bug," which is not a svnonwaa 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 ira the two cases. Probably the anterior narrow plate on the side of the cicada's'head (Fig. ?2?, .lld) is a rudiment of the base of the true jaw, or mandible. The first bristles (aldB) are outgrowths of the mandibular plates, which have become detached from them and made independently movable by special sets of muscles. The second bri?'tles (M.vB) are out- growths of the maxillae, which are otherwise reduced to small lobes (M.v) 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 ira which organs may be made over ira 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, l ts 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. ? 23) , 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 (&0m) being crowded forward into the rear part of the thorax.
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INSECTS
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