n] 



EXTERNAL FEATURES AND SKELETON 



21 



In all Dragonflies the tergum is occupied by a strong sclerite, 

 the pronotum (N), divided into anterior, median and posterior 

 transverse lobes. The median lobe is generally the largest, and 

 is divided into two by a median longitudinal depression. The 

 posterior lobe may send out a slender strip descending behind 

 the epimerum on either side, and known as the postepimeral strip. 

 The propleurum is complex in the older forms, such as the Gom- 

 pkinae, where it consists of a large epimerum (epm) behind, and 

 a narrow elongated episternum (eps) in front. This latter is con- 

 stricted into an upper and a lower portion; the lower piece has 

 been named the proinfraepisternum. In' the Libellulidae (A) both 

 parts are reduced, and the episternum is undivided. The pro- 

 sternum ($1) in the older forms is a single ventral plate with expanded 



B. 



Fig. 7. Skeleton of neck and prothorax. A. Libellula auripennis Burm. B. Lestes 

 uncatus Kir by. cx procoxa ; epm proepimerum ; eps proepisternum ; 1-4 mi 

 cervical sclerites; N pronotum; ps presternum; s^^ prosternum. After 

 Snodgrass. 



antero-lateral wings, which fuse with the proinfraepisternum. In 

 Libellulidae these expansions become separated off as distinct 

 lateral pieces, the presterna (A, ps). Internally, the prosternum 

 carries a bifurcated piece, the f urea, forming the endoskeleton of 

 the prothorax. Two slender rods connect the prosternum with 

 the mesosternum, and serve to hold the prothorax in position. 

 They also restrict its mobility upon the synthorax to small 

 dimensions. 



In the Agrionidae many interesting modifications of structure 

 are to be found in the pronotum. This may take the form of 

 ornamentation as in the males of the Oriental genus Amphi- 

 cnemis, where the posterior lobe projects backwards and upwards 

 in a huge spine or it may be concerned with the process of 

 copulation. In such a case, the prothorax of the female is 



