461 



Generalised conditio its 



11. Quadrangle triangular. 



12. M3 and M4 not uniting 



distad of the arculus. 



13. Media at the top of the 



arculus. 



14. No development of the 



anal loop. 



15. No matching of the 



transverse cross-veins. 



16. Pentagonal cells numer- 



ous. 



17. Little reduction in the 



number of rows of 

 cells and little retreat 

 distad. 



18. Nodus and arculus not 



approximated. 



19. Stigma long. 



20. Stigma sometimes ab- 



sent. 



Developniental tendencies 



•^ bjo 



TJ O 



(U -— • 



+j O 



i- +-> 



o c 



Oh O 



Yes 

 Yes 



it 



V- O 



a- c 

 a. o 



No 

 Yes 



Quadrangle rectangular. 

 M;; and M4 uniting distad of 



the arculus. 

 Media descending the arcu- Yes Yes 



lus. 

 Development of the anal Yes Yes 



loop. 

 Matching of the transverse Yes Yes 



cross-veins. 

 Reduction in number of Yes Yes 



pentagonal cells. 

 Reduction in the number of Yes Yes 



rows of cross-veins be- 



t w e e n all longitudinal 



veins and retreat distad of 



the rows. 

 Approximation of the nodus Yes Yes 



and arculus. 

 Stigma short. Yes Yes 



Stigma always present. Yes Yes 



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. 



Libellulidae. — 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 



