I 



BY R. J. TILL YARD. 181 



a strict study should be made, in order to discover any possible 

 exceptions to the rule laid down; though such are not likely to 

 occur, seeing that Ao forms the basal side in all known forms 

 throughout the series. 



The distal side of Cual is Cu.3. It is, therefore, not homologous 

 with the distal side of the anal loop of the ^Eschnhiff, which is 

 formed from Aj, or more strictly from the fusion of Aj with 

 Cuo for part of its length, and then from Aj alone lower down. 



The midrib of Cual is a cubital supplement (Cuspl). It has 

 no true homologue in any other subfamily. The straight sup- 

 plement X, in Synthemis reyiiia, is comparable to it, but is not 

 its true homologue, since it is not formed by the fusion of small 

 tracheal branches from Cu^. The midrib is strictly analogous to 

 Rspl and Mspl, the sectors developed similarly under Rs and 

 M4 respectively. 



As regards the two rival theories, our investigations have, 

 without doubt, proved the Theory of Double Descent to rest on 

 an unsound basis, since it depended upon an incorrect interpre- 

 tation of the homologies of the basal side and midrib of the 

 Italian loop. On the other hand, the Theory of Single Descent 

 is supported by the whole weight of the evidence obtained from 

 the study of the nymphal wings. 



Before passing on from the study of the anal loop, one more 

 problem presents itself, viz., the question of the phylogeny of the 

 reduced forms of the Lihellulidce. Only one larva is obtainable, 

 that of Cordulephya j)yy^n(Ea Selys, a form in which the imago 

 has an extremely reduced and narrowed hindwing, with an anal 

 loop comprised by only two large cells. I have already indicated 

 my belief* that this loop is a reduction from a more normal loop, 

 and must be considered as a very highly specialised offshoot of 

 the Eucorduliini. Let us now see what evidence is afforded by 

 the nymphal wing. 



Fig. 13 shows the anal area of this larval wing. The reduction 



from a considerably broader wing is very evident (as in the 



Zygoptera; see Plate xii., fig.l) by the fact that the imaginal 



wing-border is drawn in, leaving a broad space below, into which 



* "On the genus Cordulephya" These Proceedings, 1911,xxxvi., p.388. 



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