220 WING-VENATION IN ZYGOPTEROUS DRAGONFLIES, 



opinion regarding the unbranched radius is tentative; I am ready 

 to give it up at any serious evidence for the contrary." 



Finally, after studying the photographs of the wings of 

 Diphlebia which I sent him, and which I pointed out were con- 

 clusively in favour of the new theory, he wrote : "I now think 

 that the Unbranched Radius Theory will win the day." 



I may add that the study of Diphlebia and Calopteryx at once 

 convinced me that we had to deal, in the Zygoptera, with an 

 originally unbranched radius, which has remained unbranched 

 right down to the present day. We may summarise the evidence 

 for this under three headings, as follows : — 



1 . Direct Evide7ice from the Larval Wings. 



In every Zygopterid larval wing so far examined* 'and these 

 by now amount to a considerable number of genera), R is un- 

 branched, and M has one branch more than in the A7iisoptera. 

 The differences between C alopterygidoi, Agrionidce, and Lestidoe 

 are distincc, but of a lower order of significance. They may be 

 stated thus : — 



{a). Calopterygidce — M gives off three branches in rapid suc- 

 cession close to the arculus, and a fourth at the level of the sub- 

 nodus. 



(b). Agrionidai — M gives off one branch at the arculus, two 

 more at about the level of the subnodus, (one usually exactly 

 below it), and a fourth placed more or less distad from the sub- 

 nodus. 



[c). LestidcB —M gives off two branches close to the arculus; 

 the third and fourth come off distad from the subnodus by means 

 of a common stem, which soon bifurcates. From the lower of 

 these two branches, a long bridge is developed backwards towards 

 the main stem of M. 



2. Ontogenetic Evidence. 



We know the condition of R in the last two instars of Calo- 

 pteryx, in the last three instars of Diphlebia, and in the ]a,st four 

 stages of Austrolestes. Earlier than this, I have not been able 

 to go, the tracheation being too feeble to deal with. In all of 



* With the doubtful exception of the problematical Neosticta. 



