xxxiii, '22 | ENTOMOLOGICAL NKVVS 45 



New Researches upon the Problem of the Wing- 

 Venation of Odonata. 



I. A Study of the Tracheation of the Larval Wings in the Genus 

 Uropetala from New Zealand 



By R. J. TILL YARD, M.A., Sc.D. (Cantab.), D.Sc. (Sydney), 

 F.L.S., F.E.S., Entomologist and Chief of the Biological 

 Department, Cawthron Institute, Nelson, New Zealand. 



(Continued from page 7) 



We may now ask, what position does the family Pctalnridac 

 hold in the evolutionary line of the Odonata, and what are the 

 successive stages in the evolution of the vein Ms ? These ques- 

 tions can be very clearly answered, as follows : 



(A) The first true Odonata had entirely lost their original 

 Rs as a distinct branch of R. I shall show later, from a study 

 of the Palaeodictyoptera and Protodonata, that this original 

 Rs arose from R close to the base of the wing, as in other 

 archaic types of insects, and that it was captured and cut off 

 from R by an upwardly arching branch of M , of the type 

 found in many Palaeodictyoptera and in all Orthopteroidea. 

 The vein so formed, after its severance from R, had the 

 appearance of a six-branched media ; but one of the original 

 branches, Mia. has become degraded in the highest forms of 

 Odonata. leaving us with only fire recognizable main branches. 

 The best designation for this composite vein would be 

 the radio-median, with the notation RM ; but I do not propose 

 to adopt this new notation until I have fully established, from 

 the fossil record, the proof of its complete nature. 



(B) This original condition, which became established with 

 the rise of the Protodonata, is continued to the present day, 

 without change, into the whole of the Order Zygoptera, with 

 the single exception of the Lestidac. In all living forms which 

 have this primitive condition, the Jarral tracheation of this 

 portion of the "viny agrees eractlv "^'itli the subsequent iina</- 

 inal I'cnation; and this, I take it, is additional proof, if such is 

 needed, that neither the tracheation nor the venation of this 

 portion of the wing, in these insects, has ever become special- 

 ized. 



