BY R. J. TILLYARD. 201 



and allow of tlie introduction of short supplementary sectors 

 (Plate xii., fig. 7). As in Anisoptfira, forewings can be distin- 

 guished from hindwings easily by the fact that they are only 

 heavily pigmented from the costal border to Mj. All the rest of 

 the wing, being covered by the hindwing, is pale and very little 

 pigmented. Tlie erect position of the wing-cases, seen in adult 

 Zyyopterid larvie, is only assumed after the last ecdysis, at a 

 pei-iod sliortly before the final metamorphosis. Anisopferaheh^wa 

 in the same way, but the change is perhaps not so noticeable. 



For general study, forewings may be preferred to hindwings, 

 since they yield much clearer photographs. But for the stud}^ 

 of the anal trachea, the hindwing should be selected, since it is 

 broader at tiie base, and shows the four-branched condition much 

 more clearly. 



Much more remains to be done in the study of the nymphal 

 wings of this interesting Suborder. The present rese'arch is 

 only a bare beginning, on whicli, it is to be hoped, other investi- 

 gators will be able to build. Particularly in the Calopterygidce 

 must careful study be made of all possible nymphal wings; for it 

 is just amongst these archaic end-twigs that we may expect to 

 find the missing steps in the development of Rs across Mj and 

 Mo, and in the reduction of the anal trachea. 



We may profitably conclude this section b}^ a short discussion 

 on the question of the classification of the Suborder Zyyoptera. 



It becomes now more than ever apparent that the Selysian 

 division into Calopterygidce and Agrioiiidce is quite untenable as 

 a natural dichotomy. More than this, it is pretty clear also that 

 the Zyyoptera are not, like the Anisoptera, derived from any 

 original pure line of descent. Triangle-formation most certainly 

 only started once; and, however far back new fossil discoveries 

 may take us as regards the first formation of the triangle, there 

 can be no doubt about the origin of all Anisoptera from that 

 single line of descent, which Palaeontology already places as far 

 back as the Trias, and which probably began in the Permian 

 period. Most of the Zyyoptera {cQvtdJinly a^W those with regular 

 quadrilaterals) must have branched away from the Anisoptera- 

 line before this. But who can tell how many separate branch- 



