460 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXV. 



this and the posterior border of the cubitus, is known as the " anal tri- 

 angle" and is usually only present in the hind wing. In the hind wing, in 

 the majority of the Anisopteridse, (as shown in the diagram given on Plate 

 III.) three nervures " x, y and z", will be seen springing from the 9th 

 nervure and the posterior border of the cubitus, directed backwards to- 

 wards the termen and all nieeting in a point just before the terminal 

 margin of the wing. The " loop", as it is called, thus formed, is important 

 both for classification and descriptive purposes. The reticulation of the 

 Avings formed by a network of small cells or " areoiets" is more or less 

 close or open in the different species. Usually the wings are clear or 

 hyaline but in many species they are marked or beautifully coloured, often 

 with brilliant, metallic hues. 



In not a few species, this colouration is found to be limited to the hind 

 wings, a circumstance which may be explained by a study of the method of 

 flight adopted by these insects. During flight the fore wings only are 

 used for propulsion, the hind functionating as a pair of supporting planes, 

 thus whilst the fore — are in rapid vibration and almost invisible, the hind 

 wings are held practically motionless, exhibiting their vivid colours to the 

 full advantage. This method of flight explains also the differences in shape 

 between the fore and hind wings of the Anisopterid;«. The fore are narrow 

 so as to oS^er the least resistance to the up-strokes, the hind are broadened 

 to afford a large supporting surface. The flight of some of the Calopteryg- 

 ines as they skim over the surface of the water, the fore wings practically 

 invisible, the hind spread out, almost motionless, scintillating with brilliant 

 metallic hues, is one of the most beautiful sights that Nature affords. 



In order to simplify and render more workable the identification of 

 specjies, the nomenclature of the wing parts has been considerably modified, 

 it is therefore necessary to give the following table which compares the 

 adopted with the Selysian and Needhani notations : — 



Simplified nomenclature. 



Costa. 



Subcostal nnrvure. 



Intercostal nervure. 



Antenodal nervures. 



Postnodal nervures. 



Node. 



Subnode. 



Bridge or Subnodal triangle. 



Bridge nervures. 

 Sectors of arc. 



Subcostal space. 



Superior costal space. 



Inferior costal space. 



Trigone. 



Hypertrigone. 



Subtrigone. 



Termen. 



Tornus. 



Anal triangle. 



Loop. 



Mid-rib of loop. 



Outer border of loop. 



LnuT border of loop. 



