THE LEGS OF A BEETLE. 



17 



tr 



may be either sparsely, moderately or thickly clothed with hairs or 

 pubescence, which may be prostrate, suberect or erect in position. 

 When the pubescence is wholly absent and the surface bare they are 

 said to be glabrous. 



The hind pair, known as the inner or true wings, of beetles are 

 membranous and attached to the metathorax. They are usually so 

 arranged as to form a joint near the apex so that the entire wing 

 can be folded under the elytra. In some species with short wing- 

 covers the inner wings extend straight along the dorsal surface of 

 the abdomen. Frequently they are abbreviated or wholly absent, 

 in which case the metasternum is usually short and the elytra close- 

 ly united or connate along the suture. 



The Legs. As already noted the three pairs of legs possessed 

 by the mature beetle are joined respectively to the under surface 

 of the pro-, meso- and metasterna. The first joint of each leg, or 

 that by which it is attached, is called the coxa (plural 

 coxa?) . These vary much in shape and size and their 

 form is therefore of great importance in classification. 

 The front coxal cavities are formed by the prosternum 

 and its epimera or side-pieces. The middle coxae are 

 surrounded by the meso- and metasterna and, in some 

 Carabidae, by the epimera of the former. The hind 

 coxae are placed between the metasternum and the 

 first segment of the abdomen. 



At the outer end of the coxa and between it and 

 the femur is a small piece called the trochanter. This 

 is usually situated in the axis of the thigh and varies 

 much in form, being more or less obliquely cut off. 

 The first long piece of the leg is the thigh or femur 

 (plural femora) ; following it is the shank or tibia 

 (plural tibia-) , the junction of the two being called the 

 knee. Both of these may be more or less toothed or 

 spined and the tibiae usually bear at their outer or 

 lower extremity one or two movable spines called 

 tibial spurs. Attached to the tibiae is the foot or 

 tarsus (plural tarsi), consisting of from one to five 

 pieces placed end to end, though sometimes overlap- 

 ping. The number and form of these tarsal joints 

 varies exceedingly. The greatest number is five, and 

 when one disappears it is usually lacking on all the 

 tarsi. However, in one large group, the Heteromera, 

 the front and middle tarsi each have five joints, while the hind ones 



tb 



cl 



Leg 



a beetle, Calosoma 

 calidum. c, coxa; 

 tr, trochanter; f, 

 femur; tb, tibia; s, 

 tibial spur; t 1 ^', 

 tarsal joints; cl, tar- 

 sal claws. 

 (After Folsom.) 



