66 THE STUDY OF INSECTS. 



The principal veins are indicated by Roman numerals, 

 and when these veins are branched, the branches are indi- 

 cated by Arabic indices appended to the Roman numeral. 

 Thus the branches of radius are designated as III,, III,, III,, 

 etc. (Fig. 79). 



Figure 78 represents the fore-wing of a butterfly (Danais], 

 and Figure 79 the two wings of a moth (Castnid). In all 

 butterflies and moths veins IV and VI are wanting, and in 

 all butterflies and in many moths the basal part of vein V is 

 also wanting. The arrows in Figure 78 indicate the po- 

 sition of the remnants of this part of vein V. In the hind 

 wing of the moth figured, vein V, has become joined to vein 

 III, so that it appears to be a branch of it ; and in the but- 

 terfly vein V 3 appears to be a branch of vein VII, although 

 a short stump, indicated by the lower arrow, shows its former 

 position, in ancient butterflies, before the loss of the basal 

 part of vein V. 



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 (CJirysididce) there are usually only three or four 

 visible, while in many other insects nine appear. Except in 

 the lowest order of insects (Thysanurd) 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 setce. Frequently also the body is furnished in the male 

 with organs for clasping the claspers ; and in the female 

 with saws, piercers, 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- 



