XI] THE REPRODUCTIVE SYSTEM 223 



The Aeschninae have a complete ovipositor, differing chiefly 

 from that of the Zygoptera in the slender- 

 ness of the blades and valves, and in 

 the fact that the style carries either a 

 stiff bristle or a bunch of hairs distally 

 (fig. 100 A, br). The action of the ovi- 

 positor is here supplemented by the 

 development of a hard projecting process, 

 the dentigerous process (fig. 100 A, dp), from 

 the tenth sternite. In the Brachytronini 

 (A) this forms a plate with a curved and 

 strongly toothed distal border, projecting 

 backwards below the styles. In most Fig. 100. A. Dentigerous 



Aeschnini it is reduced to a rounded plate and styles of ^ro- 



phlebw costahs Tillyard, 

 tubercle studded with fine denticles, the $, ventral view. B. Fork 



dentigerous tuberck. In the Gynacantha ^^tn^^l 



series it becomes a sharp fork, with two, dp dentigerous plate; st 



, ,. style. ( x 6.) Original, 



three, or four prongs (B). 



The Petalurinae have an ovipositor almost as perfect as that 

 of the Aeschninae, though the processes are reduced in length. 



We may now briefly follow the stages in the reduction of the 

 ovipositor, consequent on the loss of its original function : 



(i). In the Cordulegastrinae (fig. 101) the valves are reduced 

 to minute rudiments, and the saw-teeth of the median processes 

 are absent. The terebra, however, is hypertrophied, forming 

 a very hard and conspicuous organ projecting far beyond the 

 end of segment 10. His [132] has observed these insects ovipositing 

 in rough angular debris, formed by limestone deposits in small 

 shallow streams in Switzerland. The insect flies in a vertical 

 position, dipping its abdomen into the limestone deposit at 

 intervals. Thus the hard point of the terebra protects the soft 

 parts of the end segments from injury. 



(ii) In the genus Gomphomacromia the valves are absent, 

 and the anterior processes are blunt and basally united. The 

 ovipositor appears to be at a reduction stage comparable with (i), 

 minus the hypertrophy. 



(iii) In the tribe Synihemini (fig. 102) a wide range in the 

 reduction process is still to be seen. Forms such as S. mimigenia 



