453 



Table showing Ontogenetic Tendencies of Zygoptera 

 AS COMPARED WITH Anisoptera — continued 



Egg 



Nymph 



Adult 



Anisoptera | Zygoptera | Anisoptera | Zygoptera I Anisoptera I Zygoptera 



Mesepisterna us 

 ually separated 



M e s e pisterna 

 a d j a cent or 

 separated 



Abdomen cylindrical and about 

 equal in diameter throughout ; 

 of the same diameter as the 

 thorax 



No tracheal gills Tracheal gills 

 but a long '. present 

 caudal projec 

 tion 



I M e s e p isterna 

 usually separat- 

 ed 



Wing-cases un- 

 equal in size 



Trachea of ra- 

 dial sector 

 crossing media 



Venter flat- 

 tened, abdo- 

 men much 

 broader than 

 thorax 



No tracheal 

 gills 



Ovipositor d e - Ovipositor d e 



M e s e pisterna 

 a d j a cent or 

 separated 



Wing-eases un- 

 equal in size 



Trachea of ra- 

 dial sector not 

 crossing media 



Abdomen of the 

 same diameter 

 as the thorax 



Tracheal gills 

 present 



veloped late or 

 wanting 



Rectal gills 

 present 



Folds of pro- 

 ventriculus: 4 

 large; 4 small 



veloped early 



Rectal gills ab- 

 sent 



Folds: 4 large, 

 4 small; or 8 

 large, 8 small 



M e s e pisterna 

 adjacent and 

 fused 



Wings unequal 



Radial sector 

 crossing media 



Abdomen wid- 

 ened at differ- 

 ent points, us- 

 ually of small- 

 er d i a m e ter 

 than thorax 



No tracheal 



gills 



Ovipositor some- 

 times well de- 

 veloped ; u s - 

 ually wanting 



Rectal gills 

 absent 



Folds: 4 large, 

 and 4 small 



M e s e pisterna 

 adjacent and 

 fused. 



Wings unequal. 



Radial sector 

 crossing media. 



Abdomen equal 

 thro ughout; 

 always of 

 smaller diame- 

 ter than tho- 

 rax. 



No tracheal 



gills. 



Ovipositor a 1 - 

 ways well de- 

 veloped. 



Rectal gills 

 absent. 



Folds: 8 large, 

 and 8 small. 



PHYLOGENETIC COMPARISON OF ZYGOPTERA AND ANISOPTERA 



Several important theories and rules of procedure should be men- 

 tioned before undertaking a discussion of the suborders from a phylo- 

 genetic standpoint. 



I. — Ontogeny repeats phylogeny. This is a well-recognized prin- 

 ciple and is the foundation of much phylogenetic work. 



II. — All testimony should be corroborative if properly under- 

 stood ; or iti other words, there should be no real conflict in the phylo- 

 genetic evidence obtained from different sources. 



