li'iT.] • 213 



stands revealed, and a proper understandiug of the constitution of the " anal 

 k)op " in the hind wings of Anisoptera has been arrived at. It is not at'all 

 certiiin, however, that the phyhigeny of the nodus, as deduced h'om the unusual 

 condition of that structure in tlie fos^'il Mesophlehia (p. 54), will meet with such 

 ready acceptance. As the nodal region of the wing is figured (fig. 19, C), one 

 might almost be excused for seeing in what is called the "nodal cross-vein" an 

 anterior branch of the radius, which has abruptly terminated the course of the 

 subcosta, and so brought about the characteristic break in the costal margin. 

 The subnodus, which has been regarded hitherto as the base of the radifil 

 sector, is now looked upon, alternatively, as a modified cross-vein, so that two 

 different explanations of the same structure are put forward at one and the 

 same time. Again, one meets with a highly debateable proposition which will 

 be familiar to those who have followed Tillyard's most recent writings, but 

 which one would not have desired to see stated, without qualification, in a 

 text-book for students not possessing any previous acquaintance with vena- 

 tional problems. It will be found embodied in the definition of the Siib-order 

 Zygoptera (p. 273), in the following terms: — " Radius unbrauched. An extra 

 branch of the media (the Zygopterid sector Ms) takes the place of Rs in the 

 Anisoptera. No bridge or oblique vein (except in Lesf.idae)" Although our 

 author admits that the Anisoptera have the radial sector two-branched and 

 the media not more than four-branched, he contends that in the Zygoptera the 

 radial sector is without any branch, while the media has as many as five 

 branches. In other words, upon the same six longitudinal veins, which to- 

 gether form the radius and the media, he places one interpretation for the 

 Zygoptera and another for the Anisoptera. In addition to the balance of prc- 

 baltilities involved here, a further indication that the six veins in question are 

 really homologous, and not merely analogous, in the two groups may be found 

 in the possession of a bridge and oblique vein by Epiophlehia and undoubted 

 Zygoptera like Chlorolestes, Sijnlcsfcn, and the Lestinae. All Anisopterous 

 wings exhibit the oblique vein and bridge, characters which all are agreed are 

 intimately associated with the presence and peculiar position of the radial 

 sector in that Sub-order. Notwithstanding the original ontogenetic evidence 

 which Tillyard has brought forward in support of his interpretation of 

 Zygopterous venation, it is difficult to resist the conclusion that these special 

 cliaracterSjlike the more general considerations previously discussed, must have 

 the same signification in the Zygoptera as in the Anisoptera. 



In his classificatiou of the Zygoptera, Tillyard adopts the bold expedient 

 of referring to the single family Lestidae nil the forms mentioned above as 

 possessing a bridge and oblique vein (p. 276). It is not at all clear, however, 

 that by so doing we get a natural group. AVhile the much-discussed insect 

 EphpJilehia superstcs Selys, undoubtedly resembles the Lestinae in some of its 

 chiiracters, it differs from them in other respects to such an extent that Iland- 

 lirsch considered him.yelf justified in placing it, together with certain fussil 

 genera, in a separate Sub-order, the Anisozygoptera. Another assemblage of 

 genera, the natural character of which is open to serious doubt, is the tribe 

 Libellagini (p. 284), which is now made to embrace such Neotropical forms as 

 Dicierias and IleUocharis, as well as the Ethiopian and Oriental forms which 

 properly belong to it. 



The chapter on zoo-geographical distribution will probably be considered 



