250 COLORATION [CH. 



the second abdominal segment. Brown bands of pigment are 

 often developed on the wings. This line culminates in Telephlebia, 

 Austrophlebia and Linaeschna. The effect produced is that of 

 almost complete invisibility during flight, particularly during the 

 late afternoon or early evening, when these insects usually fly. 

 I have termed this form of colouring aphantochrome (178). The 

 same tendency is manifested in a less degree in some species of 

 Aeschna and Gynacaniha. In Anax, with the adoption of a 

 sun-loving habit, the formation of heliochromes has set in. 



Hylochrome patterns of the central type are also retained in 

 the Synthemini, and in some Macromiini, besides in many other 

 genera scattered throughout the Libellulidae. In most Macromiini 

 and in the Cordulegastrinae, we meet with an advance to the 

 annulo-central type (fig. 114, d-f). Here the two pale blocks 

 fuse across the middle line, become shortened, and finally form 

 a central annulus across the segment. This type also occurs in 

 the Tetrathemini and Cordulephyini. We can contrast this with 

 the corresponding annulo-marginal type, where the annuli are 

 formed at the ends of the segment. 



In the Libellulinae, the main advance has been in the production 

 of heliochromes. These insects have forsaken their ancestral 

 forest-loving habits, and now rival the Zygoptera in their love of 

 bright sunshine. Consequently the older bicolorous pattern is 

 changed, either by substitution of bright red or orange for the 

 older yellow or green, or by the production of a metallic colour, 

 or finally by becoming changed to a unicolorous heliochrome, 

 generally bright red or pruinescent blue. The stages in this 

 latter process may be followed by studying a series of teneral and 

 mature males and females in such genera as Libellula, Orthetrum, 

 Sympetrum or Diplacodes. Taking the three common Australian 

 species of Orthetrum as an example, we see that, whereas 0. sabina 

 has retained the ancient bicolorous pattern in both sexes, in the 

 male of 0. villosovittatum it becomes overlaid with brilliant red, 

 while in the male of 0. caledonicum (and later, also, in the female) 

 it is overgrown by blue pruinescence. Metallic developments are 

 the usual rule in the Corduliinat, where the various stages in the 

 passage from an original bicolorous pattern to a uniform metallic 

 colouring may be studied in Somatochlora or Hemicordulia. 



