98 THE LARVA OR NYMPH [CH. 



so that a large supply is available for pumping into the wings. 

 These latter appear at first as small, crumpled, greenish or 

 yellowish bags. While the blood is being forced in, the wings 

 are alternately slightly opened and shut, thus aiding the pulsa- 

 tions of the heart. The expansion of the hollow bag of the 

 wing takes place with remarkable rapidity, and is a wonderful 

 example of quick growth. The basal portions expand first, the 

 wing becoming gradually smoothed out as far as a big transverse 

 crinkle marking the nodus. The apical half expands with great 

 rapidity. When the wing is fully expanded a result accomplished 

 in many cases in less than ten minutes the two wing-surfaces lie 

 parallel against one another, only actually fusing along the veins. 

 The space between the two is otherwise filled with blood plasma. 

 The presence of this fluid gives the wings a pale greenish colour, 

 while the additional refraction of the rays of light through the 

 still separated media gives a beautiful iridescence to the surface. 

 This does not disappear until the wings are quite dry and strong, 

 a consummation which takes from an hour or two to several days, 

 according to the state of the weather. The wings are generally 

 protected from damage during expansion by an outward arching 

 of the thorax, so that they hang clear of the abdomen (G). 



The assumption of the imaginal colour-pattern may be either 

 slow or rapid. In Petalura, the larval skin is very soft and un- 

 pigmented. The imaginal colour-scheme begins to shew up even 

 before emergence. By the time the abdomen has become fully 

 extended, the coloration is very vivid, rich brown and pale yellow. 

 As the insect matures, the colours become duller, the yellow 

 markings finally turning greyish, or merging into the darkened 

 brown. Many Gomphinae assume a bright black and yellow 

 colour-pattern with great rapidity, the yellow later on turning 

 to greenish or to yellowish brown. But, in most cases, the colour- 

 pattern is only slowly assumed, the imago appearing at first of 

 a peculiar pinkish fleshy tint. Brilliant heliochromes, such as 

 bright blues and reds, are often not developed for weeks. An 

 imago which has not developed its mature colouring is called 

 a tencral form. Teneral males usually resemble their corresponding 

 females in colour. 



The times given for the different stages of metamorphosis in 



