310 ZOOLOGY. 



As these parts are less complicated in the abdomen, we 

 will first study this region of the body, and then examine the 

 more complex thorax and head. The abdomen is a little 

 over half as long as the body, the tergum extending far 

 down on the side and merging into the pleurum without 

 any suture or seam. The pleurum is indicated by the row 

 of spiracles, which will be noticed further on. The sternum 

 forms the ventral side of the abdomen, and meets the pleu- 

 rum on the side of the body. 



In the female (Fig. 273, B), the abdomen tapers some- 

 what toward the end of the body, to which are appended 

 the two pairs of stout, hooked spines, forming the oviposi- 

 tor (Fig. 273, B, r, ?'). The anus is situated above the upper 

 and larger pair, arid the external opening of the oviduct, 

 which is situated between the smaller and lower pair of 

 spines, and is bounded on the ventral side by a movable tri- 

 angular acute flap, the egg-guide (Fig. 273, B, eg, and Fig. 

 276). 



The thorax, as seen in Fig. 273, consists of three seg- 

 ments, called the prothorax, mesothorax, and metathorax, or 

 fore, middle, and hind thoracic rings. They each bear a 

 pair of legs, and the two hinder each a pair of wings. The 

 upper portion (tergum) of the middle and hind segments, 

 owing to the presence of wings and the necessity of freedom 

 of movement to the muscles of flight, are divided or differ- 

 entiated into two pieces, the scutum and scutellum* (Fig. 

 273), the former the larger, extending across the back, and 

 the scutellum a smaller, central, shield-like piece. The 

 protergum, or what is usually in the books called the pro- 

 thorax, represents either the scutum or both scutum and 

 scutellum, the two not being differentiated. 



The fore wings are long and narrow, and thicker than 

 the hinder, which are broad, thin, and membranous, and 

 most active in flight, being folded up like a fan when at 

 rest and tucked away out of sight under the fore wings, 

 which act as wing-covers. 



* There are in many insects, as in many Lepidoptera and Hymenop- 

 tera and some Neuroptera, four tergal pieces i. e., prsescutum, scutum, 

 scutellum, and postscutellum, the first and fourth pieces being usually 

 very small and often obsolete. 



