AN INTRODUCTION TO ENTOMOLOGY. 



rites are in many cases obsolete, the pronotum appearing to be composed of a 

 single sclerite. In beetles and bugs the scutellum of the mesothorax is usually 

 quite conspicuous, appearing as a more or less nearly triangular piece between 

 the first pair of wings at their base (Fig. 33). Most entomological writers refer 

 to this sclerite as the scutellum. Of the four sclerites which compose the ter- 

 gal portion of each thoracic segment, the scutum is usually the largest ; the 

 scutellum is the second in importance; while thepraescutum and the postscutel- 

 lum are frequently but little developed. We find in the Hymenoptera that the 

 scutum of the mesothorax is divided into three parts by two longitudinal 

 sutures. The lateral portions of the scutum thus separated from the mesal 

 part are termed the pardpsides (i5<£ 2 ). 



Each pleurum is composed of two sclerites, arranged more or less obliquely. 

 The cephalo-ventral one is the episternum (e) ; and the caudo-dorsal one the 



Fig. 34. — Ventral aspect of a beetle, Enchroma gigantea. (See Tabular Review, p. 23, for explana- 

 tion of lettering.; 



epimeron {/). We find in many insects a third sclerite in each pleurum of the 

 mesothorax and metathorax. These sclerites when present are situated near 

 the base of the wing, and articulate with the dorsal margin of the episternum ; 

 they are the pardptera (g). In certain orders, especially Hymenoptera, the 

 paraptera of the mesothorax are small, corneous, concavo-convex scales, which 

 cover and protect the bases of the first pair of wings. By many writers these 

 paraptera are termed the tegulce, and by others the scapula. In the Lepidop- 



