BY R. J. TILLYARD. 407 



Zygopterid stock, but its nearest affinities amongst present-day 

 CalopterygidiP still need working out. 



iii. A third form of larval gizzard, also specialised, is found in 

 tlie legion Ayrion. This is another csenogenetic development 

 away from the main stock, probably later than ii., but of con- 

 siderable antiquity. 



Asthenogenesis has exerted the greatest influence on i. and iii., 

 producing such highly reduced forms as Selysioneiira, and the 

 Australian members of the legion Protoneura, on the one hand, 

 and HemiphJehia, on the other. On ii., its influence has not been 

 so pronounced. This may, of course, indicate that Lestes is less 

 archaic than we now suppose, or it may show that it is a highly 

 successful menogenetic development from a more Protoneiira-\'\VQ 

 set of ancestors, of which Lestdidea may be the only remaining 

 remnant. The latter supposition seems to me improbable. 



It is necessary to emphasise again the fact that is becoming 

 more and more evident, as the study of the Australian Odonata 

 progresses, r^iz., that forms are not necessarily archaic because 

 they are Australian. This pious article of faith will die hard 

 amongst European systeniatists, who liave so long held it im- 

 plicitly. The Australian Zyyoptera illustrate very strongly the 

 further truth, that the Australian forms of a given group) may be 

 more a'lvanced than the Palcearctic forms of the same group. The 

 Australian Lestes are clearly more advanced than their European 

 congeners. Tliey have, in fact, taken the position in nature 

 which Agriou has only just reached in Europe and Asia, while 

 our Australian representatives of the latter group show far 

 greater asthenogenetic develo[iment than their congeners of the 

 northern hemisphere. Again, our Australian members of the 

 legion I'i-/)to7ieura are more advanced asthenogenetically than the 

 main tropical stock of that legion; while our Calopterygidce have 

 progressed so far that their present-day i-epresentatives are now 

 partly classed amongst the more archaic Agrionidcp, being repre- 

 sented by the genera Diphlebia, Podopteryx, Argiolestes, and 

 Synlestes, 



