254 COLORATION [CH. 



like the mid-rib of the frond, the four outspread wings like the 

 mid-ribs of four pinnules of the frond. A transverse dark band 

 crosses the wings in a few forms. 



3. The Libellulinae. The production of an elaborate colour- 

 pattern on the wing seems to have developed in two groups of 

 this subfamily. In the more archaic forms, it appears first in the 

 Libellulini, and culminates in the Palpopleurini, Perithemis shewing 

 the highest development in the series. A much more extensive 

 production, however, took place in the more caenogenetic tribes, 

 beginning with the Sympetrini. Here we need only mention the 

 lovely Pseudoleon superbus, and the remarkable genus Neurothemis, 

 where we can trace all stages from the basal black patch in N. 

 oligoneura right up to the almost completely brown or black wings 

 of many other species. Correlated with this colour-development 

 there arises a secondary proliferation of cross- veins, apparently to 

 assist the deposition of pigment. Over three thousand separate 

 cells have been counted in a single wing in a male of this genus. 

 The females, on the whole, lag behind the males in colour-produc- 

 tion. Thus there arises the peculiar- phenomenon of venationally 

 dimorphic females, as seen in N. stigmatizans, where both deeply 

 coloured and densely-veined (homochrome) and lightly coloured 

 and open-veined (heterochrome) females are known to occur. 

 The latter is clearly the more archaic, and shews the form of the 

 genus before it went in for wing-colouring. In the Leucorrhiniini, 

 the genus Celithemis offers an interesting study in the formation 

 of beautiful wing-patterns. It is however in the lovely genus 

 Rhyothemis (Trameini) that the culmination of wing-coloration in 

 the Libellulinae occurs. These butterfly-like creatures have sacri- 

 ficed all the strength of their wonderful wing-formation for the 

 sake of producing a brilliant pattern. They are helpless fluttering 

 creatures which rise up from the ground, as one approaches 

 them, to flutter gaudily in the sunshine, or float gently to and fro 

 upon the breeze. Many of them are easily caught by hand. 

 Some forms have black wings, others brown, or brown and yellow, 

 often with lovely metallic sheen of green or purple or bronze, 

 or intricate pattern like an ancient runic script (R. graphiptera). 

 The most beautiful though by no means the most complicated 

 pattern is that of R. resplendens (Plate I, fig. 3), where about 



