ENTOMOLOGICAL NEWS [Jan., '22 



(1) The presence of a strong basal branch of Sc, which I have 

 labeled Sc'. This would seem to be the homologue of the similar 

 branch found in Plectoptera, from which the strong humeral vein oi that 

 Order is developed. Probably also a similar trachea originally under- 

 lay the anterior branch of Sc in the fossil Orders Paratrichoptera and 

 Protomecoptera, both of Triassic age. 



(2) The anal trachea, which is clearly the homologue of \A in 

 those insects in which more than one such vein is present, arises well 

 below Cu, converges towards it, and finally touches it. It then bends 

 away at the anal crossing, reaching again the level of the anal vein 

 of the imago (A'), of which the basal portion is formed, like the 

 bridge-vein, by a pigment-band only, without precedent tracheation. 

 The main stem of trachea A passes on distad to a point just below 

 the downward bend of Cul, where it meets for a short distance with 

 a very weakly formed trachea from Cid, and then bends sharply 

 away from it again towards the base of the wing posteriorly. We 

 have been in the habit of calling this weak trachea Cu2. The for- 

 mation seen in Uropetala strongly suggests, to my mind, that this sup- 

 posed trachea Cn2 is in reality not the original Cu2 at all, but a new 

 tracheal formation, which has succeeded in cutting off the distal 

 portion of \A, leaving only the turned back portions still attached to 

 the anal trachea If this is the true interpretation of these parts, it 

 would follow that Cu in the Odonata must have been originally a 

 simple trachea and vein. I shall show, in a later part of these re- 

 searches, that Cu was such a vein in the Protodonata, and that all 

 stages in the capture of the distal portion of \A by a new branch 

 descending from Cu are to be seen in the record of the Liassic Odonata. 



Plate I, fig. 2, shows the base of the hind wing enlarged, to illus- 

 trate the characters described under (1) and (2) more forcibly. 



(3) Turning next to the very important problem of the Radial and 

 Zygopterid Sectors, Plate I, fig. 3, shows, greatly enlarged, the con-' 

 dition of the tracheation of Uropetala in the region of the two oblique 

 veins for the antepenultimate instar, which was the earliest stage 

 obtainable at Cass in January. The oblique vein O, it will be seen, 

 is preceded by a very weak tracheal formation arising from R below 

 the nodus, crossing Ml and J\12 just distad of their origin from 

 Ml +2, and continuing beyond O, for only a moderate distance, alona' 

 the line of the imaginal vein called by Needham Rs. It is clearly this 

 formation which corresponds with the single oblique vein of other 

 Anisoptera. Basad from O, the line of Rs is continued backwards by a 

 pigment band only, without any tracheation. This band is connected 

 more strongly with M3 than with Ml +2, its connection with the latter 

 appearing to be more in the nature of a cross-vein at this stage. It is 

 this band which forms the bridge-vein of the Anisoptera in the imag- 

 inal stage. 



Well beyond O, there is a second oblique O'. From Plate I, fig. 3, it 

 will be seen that this is preceded, in the larval tracheation, by a very 



