4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO7 



movement than the other two pairs. But though these movements 

 are possible and actually performed by the living insect, the ordinary 

 position of the legs is lying flat against the body, and their shape in- 

 dicates that they are anatomically adapted to such position. 



The articulation of the coxae with the thorax is also modified ac- 

 cording to the described conformation of the thorax. The two regular 

 articulations, one with the pleuron and the other with the trochantin, 

 are both located on the anterior part of the coxal rim which is al- 

 most straight between them, curving but slightly outward. The coxae 

 do not hang from the thorax by two opposite points as a bucket from 

 its handle, but swing like the lid of a box on its hinges. As the line on 

 which the two articulations are located is almost parallel to a plane 

 passing from side to side of the insect and forms a certain angle with 

 the median line of the body, it is evident that the only kind of move- 

 ments that can be made on such articulation are a promotion-adduction 

 and its opposite, a remotion-abduction. The adduction and abduction 

 movements are secondary here, and are due only to the angle that the 

 line of the hinge forms with the axis of the body, the promotion and 

 remotion components of the movement being far more important. 



More free and complete adduction and abduction movements are 

 provided by another structure. This is a membranous fold on the ven- 

 tral side of the body, between the second episternal plate (figs. i6, 34, 

 51, 2Eps) and the first plate of the trochantin (figs. 16, 34, 51, iTn). 

 Both plates of the episternum are fastened together by a narrow strip 

 of membrane, and both plates of the trochantin are actually welded to- 

 gether. But between the second episternal plate and the first trochan- 

 tinal plate there is a wide band of flexible membrane which folds, al- 

 lowing the first plate of the trochantin to glide under the second plate 

 of the episternum. When this happens, the coxa being in its normal 

 horizontal position, a true movement of adduction takes place, the axis 

 of the coxa being driven toward the medial line of the body. It can 

 be observed in the living insect that the whole trochantin swings on 

 two articular points, one being its anterior apex which fits into the 

 V-shaped episternum, the other being the plural-coxal process. This 

 adds freedom to the coxal movement. In the prothorax, a cut that 

 divides the second plate of the trochantin into two pieces (fig. 16, 

 2Tn) provides an additional articulation and makes the movement 

 of the prothoracic coxa much freer than that of the mesothorax and 

 metathorax. 



The combination of the described movements allows the coxa to 

 move in every direction. The desclerotization characteristic of Blat- 



