BY R. J. TILLYARD. 183 



It is probable that the larval wings of all tlie narrow-winged 

 Libellidince would yield similar evidence of descent from broader- 

 winged forms. None of the larvie are, however, at present 

 obtainable. But in the exuviae of Nannophlehia and Lathrecista^ 

 which I have seen, the breadth of the hind wing-case certainly 

 suggests a descent from a broader-winged form. 



The foregoing discussion has been confined to the hindwings. 

 'Ilie forewings of the Anisoptera are not, however, without 

 interest. First of all, we notice the absence of pigmentation 

 throughout the posterior longitudinal portion of the wing-case, 

 due to the fact that the hind wing-case overlaps the forewing to 

 that extent (see Plate xi., fig.8). This may well be a contribut- 

 ing cause to the narrowing of the anal area, since absence of 

 light means absence of pigmentation, and pigmentation precedes 

 the development of the permanent venation. [Contrast the de- 

 velopment of the wings of Ephemeridce, in which the fore wing- 

 case overlaps the hind, and the forewing far outruns the hind in 

 development]. 



Secondly, changes take place as we pass from stage to stage, 

 although these changes are small compared with those in the 

 hindwing. 



In Stage 1 {^Eschnince), the four typical branches of A are 

 present, and placed in the primitive positions. Aj reaches and 

 fuses with Cua, and keeps this position through all succeeding 

 stages. 



In Stage 1{Synthemini), the final development of Ai is already 

 almost accomplished. Stage 3 being very similar to Stage 2, we 

 may study the forewings of these two stages together. We then 

 notice the following advance from Stage 1. 



As in the hindwing, Ac has come to be much closer to the 

 wing-base, while A3 has become hitched to A^. A2 keeps its 

 original position somewhat distad from Ac, while Aj is greatly 

 lengthened out, and consecjuently gives off supplementary trachese 

 downwards to supply the elongated area below it. Owing to the 

 compression of the triangle (explained above), which is already, 

 considerably advanced in Synthemis, though not so evident in 

 Austrocordulia, Aj takes a bend slightly downwards (Plate xi. 



