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, r'). The anus is situated above the upper 
and larger pair, and 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. 278, 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 scutwm 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—7. e., preescutum, scutum, 
scutellum, and postscutellum, the first and fourth pieces being usually 
very small and often obsolete. 
