l] INTRODUCTION 3 



his task, though the work on the last-named family had un- 

 fortunately not left the printer's hands by August 1914. The 

 immense task of dealing with the Libellulinae was entrusted to 

 Dr F. Ris, of Rheinau, Switzerland. As a result of more than 

 ten years' labour, he has now completed his work, in a series of 

 brilliantly conceived and executed fascicules which mark the high- 

 water level of systematic achievement in Entomology. The 

 Gomphinae, Lestidae and Agrionidae were unfortunately entrusted 

 to three German authors. Not one of these has so far made any 

 serious attempt to deal with his obligations, accepted now over 

 thirteen years ago. 



The personal influence of de Selys reacted directly upon the 

 next generation of students of the Odonata, and shewed itself in 

 an era of great activity and advancement in our knowledge of the 

 Order. There were many, including Martin and Ris, who could 

 proudly claim that they had sat at the feet of the master, and had 

 been directly fired with his spirit of enthusiasm. The younger 

 generation of Odonatologists, amongst whom I am proud to 

 include myself, owe to these men what they in their time owed 

 to de Selys. For the past twenty years, with unfailing courtesy 

 and industry, they have placed their unrivalled knowledge at the 

 disposal of all who sought it, and have lit afresh the flame of 

 devotion which we trust will now be passed on to succeeding 

 generations. Mainly owing to their endeavours, the systematic 

 study of the Odonata has been brought up to a level of excellence 

 not exceeded in any other Order ; and thus the way is now paved 

 for the biologists of the present and the future to pass on to the 

 deeper studies of the morphology and physiology of the group, 

 not by selecting, at a chance, any common type that happens to 

 be convenient, but with full knowledge of the phylogenetic position 

 of their regional fauna, and an added certainty as to the degree 

 of specialization to be expected of the types they choose to study. 



CHARACTERS or THE ORDER. 



Habits. Carnivorous in all stages. Amphibiotic : the larva or 

 nymph being aquatic, breathing by means of tracheal gills ; the 

 imago being aerial and breathing air directly through spiracles. 

 Hemimetabolous : the larva active, campodeiform, with no true 



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