NORTH AMERICAN ODONATA. 



211 



With the Perlina the Odonata have little more in common than 

 as stated above ; however, the former have three-jointed tarsi and 

 the mouth-parts function as biting organs, although in structure they 

 are quite different from those of the Odonata ; the Perlina have 

 eight pairs of abdominal ganglia. 



While, therefore, the Odonata are more nearly related to the 

 Ephemerina, the differences separating the two groups are still con- 

 siderable. 



As the common ancestral forru of the Perlina, Ephemerina and Odonata, 

 Mayer suggested the ProtampMbion characterized by having eleven free abdom- 

 inal segments, prothorax freely movable, head fixed, biting mouth-parts, wings 

 equal, three ocelli, tarsi five-jointed, three thoracic and seven abdominal ganglia, 

 20-50 Malpighian tubules, no ovipositor (legescheide) ; development with inter- 

 nal germinal band, larva with three pairs of legs, similar to the imago (Jen. Zeit. 

 Naturw. x, p. 202, 1876). 



The Odonata also possess primitive Insectan features in that the 

 embryo is developed from an invaginated germinal band, recalling 

 the manner of development of the Myriapods (Korschelt and Heider 

 18), and in the preservation throughout life of ten distinct abdominal 

 segments with a terminal anal segment — a number which appears to 

 be constant for the early embryonic stages of all insects. 



RELATIONSHIPS OF THE ODONATE GROUPS TO EACH OTHER. 



The writer's view of the relationship of the subfamilies of the 

 Odonata to each other may be best expressed by the accompanying 

 diagram, in which the Calopteryginse are represented as the most 



Cordulinfe Libellulinae 



Goraphiiia 



Cordulegasterinse 

 Ae.schninae 



Agrioniiiae 



-Calopteryginie 



primitive and least specialized. That at least some Calopteryginii? 

 are less specialized than all the other Odonata, or in other words 

 differ less from other Insects, seems to be indicated by the simulta- 



TRANS. AM. ENT. SOC. XX. AUGUST. 1893, 



