2 A VENATIONAL STUDY OF THE ZYGOPTERA 



III. Tendencies in Specialization 26 



Vein Reduction 27 



1. Reduction in the number of supplementary sectors 27 



2. Reduction of the veins Cu2 and Cui 28 



3. Decrease in the number of antenodal cross-veins 28 



4. Decrease in the number of postnodals 29 



5. Loss of the cross-veins in the quadrangle and subquadrangle 29 



6. Reduction in the number of those antenodal cells situated between M4 



and Cui 29 



7. Reduction in the number of cross-veins behind the anal vein 29 



Vein Shifting 30 



1 . Narrowing of the wing 30 



2. Progressive petiolation 31 



3. Retraction of the nodus toward the base of the wing 31 



4. Tendency for M2, Rg, and INIs to arise nearer the tip of the wing and 

 further from the subnodus 31 



5. Migration outward of the base of Mia 33 



6. The position of the second antenodals before the arculus 33 



7. The tendency for the quadrangle to become acute distally 33 



8. Change in the length of the quadrangle 35 



9. Attachment of supplementary sectors 35 



10. Straightening of the longitudinal veins 35 



1 1 . Matching up of the cross-veins in transverse series 36 



Aliscellaneous Features 36 



1 . Differentiation of fore and hind wings ; 36 



2. The bracing of the stigma 36 



3. Atrophy of the stigma 37 



IV. Summary ' 37 



V. Keys for the Identification of Genera 38 



The Anisozygoptera 40 



The Zygoptera 40 



The Agrionidae 40 



The Polythorinae 42 



The Agrioninae 42 



The Epallaginae 45 



The Disparocyphinae 47 



The Coenagrionidae ^ 41 



The Lestinae 48 



The Lestoidinae 49 



The Pseudostigmatinae 49 



The Megapodagrioninae 50 



The Coenagrioninae 53 



The Protoneurinae 63 



. VI . Bibliography 67 



VII. Plates 72 



