461 



>. 



4"^ i! bjo 



"9 o "p c 



Generalized conditions Developmental tendenaes V. ° X. o 



CL, o & c 



II. Quadrangle triangular. Quadrangle rectangular. Yes No 



. 12. Mg and M4 not uniting M-, and M4 uniting distad of Yes Yes 

 distad of the arculus. the arculus. 



13. Media at the top of the Media descending the arcu- Yes Yes 



arculus. lus. 



14. No development of the Development of the anal Yes Yes 



anal loop. loop. 



15. No matching of the Matching of the transverse Yes Yes 



transverse cross-veins. cross-veins. 



16. Pentagonal cells numer- Reduction in number of Yes Yes 



ous. pentagonal cells. 



17. Little reduction in the Reduction in the number of Yes Yes 



number of rows of rows of cross-veins be- 

 cells and little retreat t w e e n all longitudinal 

 distad. veins and retreat distad of 



the rows. 



18. Nodus and arculus not Approximation of the nodus Yes Yes 



approximated. and arculus. 



19. Stigma long. Stigma short. Yes Yes 



20. Stigma sometimes ab- Stigma always present. Yes Yes 



sent. 



The different families are specialized in the characters listed under 

 the figures following them : — 



Coenagrionidae.— 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 16, 17, 18, 19, 20. 



Agrionidae. — 11, 15, 16. 



Aeshnide. — 2, 5, 11. 



Gomphidae. — i, 5, 7, 11. 



Libeflulidae. — i, 12, 13, 14. 



From the above it will be seen that in wing venation the family 

 Coenagrionidae is by far the most highly specialized, while the Agrion- 

 idae, Aeshnidae, and Gomphidae are about equally specialized, and 

 the Libellulidae are intermediate in position. 



29. — The primitive abdomen consisted of a cylindrical portion of 

 the same diameter as the thorax; and the same is now essentially true 

 of the nymphs of Zygoptera. In the adults, however, the diameter 



