254 



Anvals of the 8o7tth African Museum. 



microscopic stiff bristles along the veins ; wlieu coloured the various 

 tints result from tlie pigmentation of the wing membrane itself, or 

 from some waxy exudation. The pigmentation niostlv results in tints 

 from clear yellow through brown to deep black, often with metallic 

 lustre ; in some cases also blood-red may occur. Waxy exudation 

 produces an opalescent white, or bluish when on a background of 

 black. But the immense majority of the dragouHy wings are hyaline 

 or bear only small basal coloured spots. 



The venation of these wings is of the utmost importance to the 

 systematist. From tlie early times of odouatology some of the more 



-Crocothemis erythraea. Lateral view of thorax. Lettering as in 

 Text-fig. 4. 



obvious features have been adopted as distinctive characters for the 

 larger systematic vinits ; but in more recent times patient investigation 

 of many minute (but often morphologically significant) details has 

 shown that characters for the smaller groups, down to genera and 

 sometimes even to species, may be drawn with great advantage from 

 the neuration. An advantage is to be found in these characters 

 being common to both sexes of one species or genus (unlike many 

 other important distinctive characters in dragonflies), and in their 

 being easily described and exactly figured, especially by photography. 

 The introduction of ]ihotogi'apliy into the descriptive scheme of our 

 modern odouatological literature is undoubtedly one of its distinctive 

 features when confronted with the writings of the classical time, and 



