4:^0 ON THE GENUS CORDULEPHYA, 



higher animals in Australia been subjected, in the same 

 degree, to the strenuous competition with immigrants that 

 the autochthonous Odonata have had to undergo. 



As the reducfioii-process alonr/ a new line of development , 

 which has been the main factor in evolving Cordulephya, is 

 of the greatest importance, I propose the term asthenoyenesis 

 (Gr. MrOei'ij'i, weak) for it, in contrast to specialisation in 

 development of parts to form sfroiif/er types, such as has been 

 tne main line of development of the LihelluUda. The latter 

 may be termed menoyensis (Gr. /xei-o?, strength). Thus, we 

 should say that the Anisoptcra as a whole are the menogenetic 

 group, the Zyyopft ra. the aathenoyenetic group of Odonata. 

 A race may follow a menogenetic line of development up to 

 a certain standard, and then, like Cordulephya, adopt an 

 asthenogenetic line. It is, of course, possible, though less likely, 

 for the opposite to happen. 



Note B. — On the "quadrilateral" genera of the Lire l. 

 LULiD>E. - It seems very open to doubt whether the four-sided 

 triangle, at present found in some of the Libellulid genera, is 

 in any case an archaic structure. It should be borne in mind 

 that the Anisopter'ul triangle was formed at a period of 

 intense energy and development amongst the Odonata, when 

 the group probably occupied a far more dominant position 

 amongst the Insecta than it does now. That being so, races 

 that remained half-way, adopting neither the anisopterous 

 nor the zyyopterous tendency in full, must very soon have 

 become extinct. The present-day "quadrilateral" LiheUu- 

 lidce are all (except I'eNtaf/ienns, an admittedly specialised 

 form) small species in comparison with their nearest related 

 forms. That being so, it is important to enquire how far 

 asthenogenesis has affected them. If the larvae are found to 

 be highly developed, and the imagines, apart from the tri- 

 angles, shew a general absence of archaic characters, the 

 balance of evidence is surely in favour of their being astheno- 

 genetic members of the more highly specialised groups. In 



