222 THE REPRODUCTIVE SYSTEM [CH. 



The three pairs of processes may be named anterior processes 

 (ap), lateral processes or valves (v) and median processes (mp) 

 respectively. The anterior processes (ap) are two sword-shaped 

 structures, slightly curved, and with a short saw-like edge near 

 the pointed distal end. Each process is fixed to a short base-piece, 

 an outgrowth of the posterior part of the eighth sternite. Into 

 these pieces are inserted the muscles whose contractions cause 

 the ovipositor to emerge from its sheath. Together with the 

 median processes, the anterior processes form that part of the 

 ovipositor known as the aculeus or terebra. 



The lateral processes or valves (v) are of a very different form, 

 being rather broad, leaf -like, slightly convex lamellae. Their bases 

 occupy the whole length of the ninth sternite, from which they 

 are developed. The apex of each projects postero-ventrally under 

 the tenth segment. At its end it carries a hard, pointed organ 

 called the style, styloid process, or sternorhabdite (st). The structure 

 of the style shews that it is a tactile organ. The outer border 

 of the valve is finely denticulate, and there is a large tooth close 

 to the style. 



The median processes (mp) somewhat resemble the anterior ones, 

 but the blade is narrowed in the middle, and the distal end carries 

 a complicated set of saw-like teeth. The process is inserted into 

 a short base-piece arising from the inner anterior side of the 

 base of the corresponding valve. Into these base-pieces are 

 inserted the muscles which retract the ovipositor back into its 

 sheath. 



From the above description, it is clear that the complete 

 ovipositor of the Dragonfly is an archaic structure, homologous 

 with the well-known form such as is found in the Sawflies. All 

 the Zygoptera possess ovipositors closely resembling that of 

 Synlestes, though seldom so highly developed for cutting. In the 

 Calopterygidae, the organ is not so large in proportion to the size 

 of the insect, but the parts are closely similar. In some Agrioninae 

 (e.g. Ischnura) there is a ventral spine developed posteriorly on 

 the eighth sternite, projecting under the base of the ovipositor. 

 In many forms the valves are crossed by a diagonal ridge running 

 to the style. A bunch of stiff hairs often takes the place of the 

 large tooth seen in Synlestes. 



