66 
THE STUDY OF INSECTS . 
the five branches of the typical radius, or vein III, are 
designated either thus, R u R 2 , R 3 , R 4 , R 5; or thus, m u 
III 2 , Ills, III4, Ills- 
When two or more branches of a branched vein coalesce, 
the compound vein is designated by an expression indicating 
this coalescence, as III2+8 or R 2+8 . In this way it is possible to 
indicate some of the changes that have taken place in the de¬ 
velopment of the species; and to make use of them in working 
out the classification of the group to which the species belongs. 
The cells of the wing are designated by applying to each 
the number or the abbreviation of the name of the vein that 
forms its cephalic (front) margin. In Figure 78 the veins are 
designated by numbers at the margin of the figure ; the cells 
by numbers within the figure. When a cell is divided by a 
cross-vein the parts are numbered, as in the case of cell V 2 in 
Figure 497, page 422. 
The Abdomen and its Appendages. 
The abdomen is the third or caudal region of the body. 
Its segments are more simple, distinct, and ring-like than 
those of the other regions. The number of segments of 
which it appears to be composed varies greatly. In the 
Cuckoo-flies ( Chrysidida ) there are usually only three or four 
visible, while in many other insects nine appear. Except in 
the lowest order of insects ( Thysanura ) the abdomen of the 
adult bears no locomotive appendages. But many larvae 
have fleshy appendages which aid in locomotion : these are 
termed prolegs . In the adult the end of the body in many 
families is furnished with jointed filaments—the cerci } and 
caudal setcz. Frequently also the body is furnished in the 
male with organs for clasping—the claspers ; and in the female 
with saws, pierces, or borers—the ovipositor . In the female of 
certain insects there is a sting , a modified ovipositor, which 
is used as an organ of defence ; and the abdomen of plant- 
lice and certain other insects bears a pair of tubes or tuber- 
