276 PRACTICAL LESSONS IN SCIENCE. 



The mouth parts consist of the labrum or upper lip; the 

 mandibles or larger jaws; the maxillse or lesser jaws, to which 

 are attached little jointed bodies called maxillary palpi; and the 

 labium or lower lip, to which are attached a pair of jointed 

 bodies called labial palpi. These are the mouth parts of biting 

 insects, but some have the maxillae and labium more or less 

 modified so as to fit them for licking or sucking up liquids. 

 Sometimes the first maxillae are changed into a sucking tube, as 

 in butterflies and moths. Sometimes the labium forms a tube 

 and the maxillae forms cutting parts to open the way for the 

 sucking tube, so that the mouth appears in a great variety of 

 interesting forms. 



The thorax consists of three segments, prothorax, meso- 

 thorax and metathorax. The appendages of the thorax are 

 the legs and wings. All true insects have a pair of legs jointed 

 to each segment of the thorax. Each leg consists of basal joint 

 or coxa, the femur, the tibia and the foot or tarsus, which may 

 be armed with a pair of claws. The legs vary widely in form and 

 size, depending mainly on their use. The wings arise from the 

 second and third parts of the thorax. They are considered by 

 many as simply expansions of the integument spread out over a 

 framework of horny tubes. The tubes are really double, consist- 

 ing of a central air tube inclosed in a larger tube which is filled 

 with blood , so that the wings serve the double purpose of organs 

 of locomotion and respiration. In some cases the anterior wings 

 are thickened and hardened by the deposition of horny matter 

 so as to form a protecting case for the other pair of wings and 

 for the abdomen. 



The abdomen consists of nine or ten segments, each of which 

 is made up of a dorsal and a ventral plate. The segments are 

 joined together by soft connecting membranes, and the parts of 

 the segments are united in the same manner, so that the abdo- 

 men is capable of considerable expansion. At the extremity of 

 the abdomen there are terminal appendages, as stings, appa- 

 ratus for depositing eggs, and other organs pertaining to the re- 

 productive process. 



