104 



LEGS 



superior, the wings. The legs are always six in number, and are 

 usually present even in larvae, though there exist many apodal 

 larvae, especially in Diptera. The three pairs of legs form one 

 of the most constant of the characters of 

 Insects. They are jointed appendages and 

 consist of foot, otherwise tarsus ; tibia, femur, 

 trochanter, and coxa ; another piece, called 

 trochantiii more or less distinctly separated 

 from the coxa, exists in many Insects. The 

 legs are prolongations of the body sac, and 

 are in closer relation with the epimera and 

 with the episterna than with other parts 

 of the crust, though they have a close 

 relation with the sternum. If we look at 

 the body and Isg of a neuropterous Insect 

 (Fig. 58) we see that the basal part of the 

 leg the coxa is apparently a continua- 

 tion of one of the two pleura! pieces or of 

 both; in the latter case one of the prolonged 

 pieces forms the coxa proper, and the tip 

 of the other forms a supporting piece, 

 which may possibly be the homologue of 

 FIG. 58. Hind leg of Pan- the trochantiii of some Insects. In some 

 o^a:,episternum;a;, Qrthoptera, especially in Blattidae, and in 



epimeron ; o, coxa ; o , t * < _ 



coxal fold of epimeron ; Termitidae, there is a transverse chitinised 

 c, trochanter;^ femur; f M interposed between the sternum and 



e, tibia, ; f, tarsus. 



the coxa, and this has the appearance of 



being the same piece as the trochantin of the anterior legs of 

 Coleoptera. 



Beyond the coxa comes the trochanter ; this in many 

 Hymenoptera is a double piece, though in other Insects it is 

 single ; usually it is the most insignificant part of the leg. The 

 femur is, on the whole, the least variable part of the leg ; the 

 tibia, which follows it, being frequently highly modified for 

 industrial or other purposes. The joint between the femur and 

 the tibia is usually bent, and is therefore the most conspicuous 

 one in the leg ; it is called the knee. The other joints have not 

 corresponding names, though that between the tibia and the 

 tarsus is of great importance. The spines at the tip of the tibia, 

 projecting beyond it, are called spurs, or calcares. The tarsus or 





