THE ANATOMY OF INSECTS. \g 



tera, the paraptera of the mesothorax are greatly developed. Here they appear 

 as leaf-like epaulets, which sometimes cover not only the bases of the wings, but 

 also the greater part of the mesonotum. In descriptive works on this order 

 they are usually termed the patdgia. 



In the membrane connecting the head with the prothorax there is on each 

 side a pair of small sclerites. These are termed \\izjugular sclerites (lAg). 



Each sternum is composed of a single sclerite. As indicated above, the 

 three sterna are designated as the prosternum (14*), mesosternum (152), and 

 metasternum (162) respectively. 



In some beetles the metasternum is divided into two unequal portions by a 

 suture which extends transversely a short distance in front of the caudal mar- 

 gin ; the smaller sclerite which borders the posterior coxae in front and often 

 passes between them is called the ante-coxal piece of the metasternum. 



i 



The Appendages of the Thorax. 



The appendages of the thorax are the organs of locomotion. 

 They consist of the legs and the wings. Of the former there are 

 three pairs ; of the latter, never more than two. The distribution of 

 these appendages has already been given (p. 16). The legs are 

 joined to the body near the lateral borders of the sterna ; the wings; 

 near the lateral margins of the terga. 



The Legs. Each leg (17) consists of the fol^i-ing-named parts 

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

 (Fig. 34). 



The Coxa. The coxa (a) is the proximal segment of the leg. It is the one 

 by means of which the leg is articulated to the body. It varies much in form, 

 but 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 (e.g. Carabidae). In such cases the coxae really form a part 

 of the body-wall, and are liable to be mistaken for primary parts of the meta- 

 thorax instead of the proximal segments of a pair of appendages. 



In certain insects there is a small sclerite between the coxa and the epime- 

 ron. This is considered an appendage of the coxa, and is called the trochaic 

 tin (a 1 ). It is more often visible in the prothorax than in the other segments?^ 



The Trochdnter. The trochanter (ti) is the second part of the leg. It con- 

 sists usual1y~oF a very short, triangular or quadrangular segment, between the 

 coxa and the femur. Sometimes the femur appears to articulate directly with 

 the coxa; and the trochanter to be merely an appendage of the proximal end 

 of the femur (e.g. Carabidae). But the fact is that in these insects, although 

 the femur may touch the coxa, it does not articulate with it; and the organs 

 that pass from the cavity of the coxa to that of the femur must pass through 

 the trochanter. In the sub-order Terebrantia of the order Hymenoptera the 

 trochanter consists of two segments. 



The Femur. The femur (c) is the third part of the leg; and is usually the 

 largest part. It consists of a single segment. 



