56 



AN INTRODUCTION TO ENTOMOLOGY 



pairs, a pair borne by each of the three thoracic segments; of the 

 latter there are never more than two pairs, a pair borne by the meso- 

 thorax and a pair borne by the metathorax. One or both pairs of 

 wings may be wanting. 



The legs. — Each leg consists of the following named parts and 

 their appendages: coxa, trochanter, femur, tibia, and tarsus. 



The coxa. — The coxa is the proximal segment of the leg; it is the 

 one by which the leg is articulated to the body (Fig. 67). The coxa 

 varies much in form, but it is usually a truncated cone or nearly 

 globular. In some insects the coxae of the third pair of legs are more 

 or less flattened and immovably attached to the metasternum; this 

 is the case in beetles of the family Carabidas for example. In such 

 cases the coxas really form a part of the body-wall, and are liable to be 

 mistaken for primary parts of the metathorax instead of the proximal 

 segments of appendages. 



In several of the orders of insects the coxa is apparently composed 



of two, more 

 or less dis- 

 tinct, parallel 

 parts; this is 

 the case, for 

 example, inin- 

 sects of the 

 trichopterous 

 genus Neuro- 

 ma (Fig. 68, 

 Cx and epm). 

 But it has 

 been shown 

 by Snodgrass 

 ('09) that the 

 posterior part 

 of the sup- 

 posed double 

 coxa, the 

 "meron"(Fig. 

 68, epm) is a 

 detached por- 

 tion of the 

 epimerimi. 

 The styli. — In certain generalized insects, as Machilis of the order 



Fig. 67. — Legs of insects: A, wasp; B, ichneumon-fly; C, 

 bee; c, coxa; tr, trochanter; /, femur; ti, tibia; to, 

 tarsus; m, metatarsus. 



