21 



PROTHORAX. 



Dorsal part (pronotum). That which may be properly 

 termed the dorsal part, of the prothorax is a large sunbon- 

 net-shaped piece which covers the greater portion of the 

 sides as well as the dorsal surface of this segment. This 

 piece is called \ht pronotum. 



It is believed that the dorsal part of each thoracic segment 

 consists typically of four sclerites. These are named, be- 

 ginning with the cephalic, prcescutum, scutum, scutellum, and 

 postscutellum. These sclerites may be distinguished in the 

 dorsal parts of the mesothorax and metathorax (inesonotum 

 and metanotum} of many insects; but the pronotum consists 

 usually of a single piece. In the insect which we are study- 

 ing, although the pronotum consists of a single piece, it is 

 crossed by three well-marked sutures, indicating the di- 

 vision into four sclerites, which may be named as indicated 

 above. 



On the latero-dorsal aspect of the pronotum the suture 

 between the praescutum and the scutum extends cephalad 

 for a short distance and is then interrupted ; the lateral por- 

 tion of this suture is parallel with and quite near to the 

 cephalic margin of the pronotum. Near the center of each 

 lateral aspect of the pronotum there is a short oblique suture 

 which separates the lateral fourth of the scutellum from the 

 mesal part of that sclerite. None of the sutures extend to 

 the lateral margin of the pronotum. 



Make a drawing of the lateral aspect of the pronotum. 



Ventral part. The ventral part of each thoracic seg- 

 ment consists typically of two sclerites, one situated in front 

 of the other ; the first is the sternum, the second, which has 

 never been named, may be termed the sternellum. The 

 sternellum is frequently divided longitudinally into two 

 parts, which may be widely separated. 



