104 



TEXT-BOOK OF ENTOMOLOGY 



the middle or normal position, and therefore describe on the whole a curve 

 of 120. The angle of turning on the middle leg hardly exceeds a legitimate 

 limit, yet a forward as well as a backward rotation takes place. The former is 



entirely wanting in the hind 

 hips ; they can only be moved 

 backward. 



The number and strength 

 of the muscles on which the 

 rotation of the hips depends, 

 correspond with these varying 

 movements of the individual 

 legs. Thus, according to 

 Straus Durckheim, the fore 

 coxa of many beetles pos- 

 sesses five separate muscles 

 and four forward and one 

 backward roll ; the middle 

 coxa a like number of muscles 

 but only two forward rolls, 

 while the hind hips succeed 

 in accomplishing each of the 

 motions named with a single 

 muscle. 



One can best see how these 

 muscles undertake their work, 

 and above all how they are 

 situated, if he lays bare the 



FIG. 114. Leg of an Aphid, with the tarsus (f) much 

 reduced : 1, 2, 3, legs of 1st, 2d, and 3d pairs. 



prothorax of the stag beetle (Fig. 116). Here may be seen first the thick 

 muscle which turns to the front the rotating axis in its cylindrical pan, and 

 thus helps to extend the leg, while two other tendons, which take the opposite 

 direction, are fitted for reflex movements. 



FIG. 115 Mechanics of an insect's leg: d, coxa, c,, axis of revolution ; a and J>, the coxal 

 museles; e, troehantcr muscle (elevator of the femur); ./', extensor, ;/, flexor, of the tihia (/>); 

 //. tibial s|iine; h. flexor. i, extensor, of the foot: k. extensor,/, flexor, of the claw; /<, 

 place nf llexnre of the tibia; y/'.y. ler after beiiiy turned l.aek by the coxa, f> l r, by the simul- 

 tani s tlexiire of the tibia The resulting motion of the end of the tibia, through the simul- 

 taneous movement (o) and revolution (mj), indicates the curve nr. After (iraher. 



In Fig. 115 the muscles mentioned above, and their modes of working, may 

 be distinguished by the arrows a and b. 



In order to simplify matters, we will imagine the second component part 



