l6 ENTOMOLOGICAL NEWS [Jan., '14 



of each segment is termed the sternum. The sclerites (either 

 distinct plates, or subdivisions of the more strongly chitinized 

 regions marked off by sutures) of the tergum are called ter- 

 gites; those of the pleural region are called l pleurites; and those 

 of the sternal region are termed sternites. Unless confusion is 

 to continue to reign in the terminology applied to the thoracic 

 sclerites we must hold rigidly to the simple and logical usage 

 given above. 



From the study of the larval forms of insects, and the more 

 primitive representatives of the order, it would appear that 

 the thoracic sclerites were originally formed as numerous 

 plates formed by depositions of pigment and chitin, due (in all 

 probability) to the stimulus of muscular tension, and to other 

 mechanical stimuli, such as friction. As specialization pro- 

 gresses, there is a marked tendency for these originally dis- 

 tinct plates to unite, or fuse together ; and by the breaking up 

 into parts (derivatives) of the original plates, by the re-com- 

 bination of these parts fusing with other sclerites, and by the 

 formation of secondary sutures (i. e. those not originally pres- 

 ent), the modifications of the original typical or "ground-plan" 

 met with in the different orders of insects, are brought about. 



The hypothetical "ground-plan" of thorax shown in Plate 

 III, Fig. 2, is more of a composite, or combination of the pos- 

 sible conditions met with in different winged insects, than an 

 attempted reconstruction of the original condition found in the 

 ancestors of these insects. It nevertheless approaches the 

 original condition, in many respects. The plates which were 

 originally separate and distinct are, for the most part, so rep- 

 resented in the figure. The greater part of the sutures origin- 

 ally present, or those early formed, are designated by heavy 

 lines; while those added as later modifications (i. e. secondary 

 sutures), are indicated by clotted lines. Although the types 

 of thoracic sclerites represented in the following series do not 

 cover all of the conditions met with in winged insects, it is a 

 comparatively simple matter to reduce any of them to some one 

 of the types here represented. The principal sclerites of the ter- 

 gal, pleural and sternal regions may be briefly described as 

 follows : 



