248 



COLORATION 



[CH. 



blocks, in which brilliant hypodermal pigment becomes developed. 

 The middle line and all the area surrounding the blocks is darkened 

 by cuticular pigmentation. 



We shall now trace the development of these basic patterns 

 in turn: 



A. Marginal Types (fig. 113). 



The most archaic marginal type still extant appears in Petalura 

 pulcherrima. Even in this archaic genus itself, the marginal type 

 rapidly tends to become altered, assuming the form which we may 

 call annulo-marginal, in which, by further growth, and later by 

 fusion of the two dark blocks of ground-colour, the hypoderm 



a. 



Fig. 113. Marginal types of colour-pattern, a, archaic type; 6, c, d, stages in the 

 development of the annulo-marginal type (d). Original. 



pigment becomes at last restricted to narrow transverse zones 

 or annuli at the base and apex of the segment, together with 

 latero- ventral patches not shewn in the diagrams. This annulo- 

 marginal type is found, amongst Anisoptera, in the Gomphinae 

 and Petalurinae, the hypoderm colouring being in all these cases 

 bright yellow, greenish-yellow or brownish-yellow, rarely reddish. 



In the Zygoptera, the original marginal type may still be 

 seen in many Agrionidae, particularly in the females. Much more 

 commonly, however, it becomes reduced to the annulo-marginal 

 type. The hypodermal pigments in this suborder are generally 

 bright blue or red, sometimes orange, pink, straw, pale green or 

 cream. Dull greens and greenish-blues predominate in the females. 



If we now compare the marginal patterns found in the 

 Anisoptera with those of the Zygoptera, we see at once that the 

 former are correlated with a forest-loving habit, the latter with 

 a sun-loving habit. We shall term the former hylochromes, the 

 latter heliochromes. In the former, the hypoderm pigment is pre- 

 dominantly green or yellow, in the latter, bright blue or bright red. 



