46 ENTOMOLOGICAL NEWS [Feb., '22 



(C) Arising from somewhere low clown in the Megapoda- 

 grionine stem, we find the first tracheational specialization still 

 in process of becoming established, in the subfamily Synlestinac 

 of the Lestidac. In these archaic insects, whose close affinity with 

 the still more ancient Mcgapodagrioninac admits of no doubt 

 whatever, we find that, in most larvae (the genus examined 

 was Synlestcs], there is a complete formation of long bridge 

 and distal oblique vein 0'. This has been brought about by 

 one of the small tracheae descending from A/2, far distad from 

 the nodus, capturing the line of the vein Ms, so that the orig- 

 inal trachea which supplied this vein from its base on M3 

 outwards becomes withered, leaving the apparent long bridge- 

 vein as the basal half of Ms. Also, Synlestes still shows the 

 archaic position of the origin of Ms, viz., from M3, though 

 most recent Zygoptera have Ms arising from Ml +2. But, in 

 a certain number of these larvae of Synlestes, one or more of 

 the wings may retain the original Megapodagrionine condi- 

 tion, i. c., there is no trachea forming the oblique vein, which, 

 consequently, is absent in the imago. 



In the subfamily Lcstinae, the oblique vein and long bridge 

 have become completely established. An exactly similar forma- 

 tion is to be seen in the Epiophlebiidae, and also in the fossil 

 genus Heterophlcbia, which is closely allied to this family. 

 Both Epiophlebia and Heterophlcbia are to be considered as 

 belonging undoubtedly to Handlirsch's Suborder Anisozygop- 

 tera, the discovery of the larva of the former genus making 

 the recognition of this Suborder a necessity, as I have shown 

 in a previous paper. 4 



(D) For the next step, we must postulate an origin for the 

 Suborder Anisoptera from forms among the Anisozygoptera in 

 which the distal oblique vein and long bridge were fully estab- 

 lished. Pletcrophlebia may not have been the true ancestor 

 of the Anisoptera, but there can be little doubt that it repre- 

 sents very closely what that ancestor was like, at the stage of 

 the first formation of the triangle in the hind wing. Starting 



4 Tillyard, R. J. "On an Anisozy gopterous Larva from the Himala- 

 yas (Order Odonata). Records Indian Museum, 1921, xxii, pt. ii, no. 

 12, pp. 93-107, pi. xiii. 



