20 



CALIFORNIA STATE COMMISSION OF HORTICULTURE. 



of several hexagonal plates, capable of motion and to which the various 

 appendages are articulated. Each of these segments bears one pair of 

 legs, but only the meso- and metathorax bear wings, and either or both 

 pairs of wings may be wanting; as in the flies there is but one pair, 

 and in many insects none. 



Legs. In most adult insects and many larvae, each of the three 

 thoracic segments bears one pair of legs, composed of several parts. 

 That joint immediately attached to the body is known 

 as the coxa, the next as the trochanter, femur, tibia, and 

 tarsus, the latter corresponding to the foot in the higher 



C Sc, Sc2Ri 



tb 



M4 



IstA 



Cu2 



3dA 2dA 



FIG. 19. Hypothetical type of venation. A, anal vein; C, costa; Cu, 

 cubitus; M, media; R, radius; Sc, subcosta. (After Comstock and 

 Needham.) 



animals. The legs are modified in many ways to meet 

 the requirements of the insect, and are adapted to run- 

 ning, leaping, swimming, burrowing, or grasping their 



.cl 



FIG. 18. Leg of a 

 beetle (Caloso- 

 ma calidurn). c, 

 coxa; cl, claws; 

 /, femur ;s, spur; 

 M 5 , tarsal seg- 

 ments; tb, tibia; 

 tr, trochanter. 



ist A 



FIG. 20. Wing of a fly (Rhyphus). A, anal vein ; C, costa ; Cu, cubitus ; 

 M, media; R, radius; Sc, subcosta. (After Comstock and Needham.) 



prey, according to the habits of the species. The tarsus is composed 

 of several parts or segments, usually five, the last one generally being 

 provided With one or two claws. 



Wings. There are usually two pairs of wings, and these are borne 

 on the last two segments of the thorax the mesothorax and the meta- 

 thorax. As above stated, either one or both pairs may be absent, but 

 when so they are usually represented by rudimentary pads or other 

 organs. In the order Diptera, or two-winged flies, a pair of small 

 hooked or knobbed organs, known as halteres, or poisers, represent 



