34 A VENATIONAL STUDY OF THE ZYGOPTERA 



shows a generalized structure and adds that for the Agrioninae 

 (Coenagrionidae here) he beHeves In two Hnes of evolutionary 

 activity, one in which MA is the center of activity and the quad- 

 rangle becomes pointed; the other in which MA is not changed, 

 but the posterior area of the wing is reduced ; here he refers of course 

 to the Protoneurinae. Dr. Calvert (1913) disagrees with the views 

 above expressed, partly because he finds no paleontological evi- 

 dence for their support. He argues that since "all the Jurassic 

 fossils, which are not clearly Anisoptera, show an oblique quad- 

 rilateral with its posterior distal angle acute," it seems "necessary 

 to regard the oblique quadrilateral as the more primitive and the 

 rectangular as a later appearance." It is true that the Anisozy- 

 goptera figured by Handlirsch have a quadrangle which is some- 

 what acute distally, and that the only living representative of. this 

 suborder, Epiophlebia, (fig. 10) has an acute quadrangle, so that 

 this condition seems the more ancient. When the living Zygoptera 

 are taken up, however, those that are in other respects the most 

 primitive have the quadrangle regular; in the Agrionidae, it is only 

 in the higher Epallaginae that the obliquity becomes noticeable; 

 and In the higher Megapodagrlonlnae, Lestlnae, Pseudostigma- 

 tinae, and those Coenagrlonlnae of the Argia and Coenagrion 

 groups it is carried to its highest development. Comparative 

 morphology, therefore, brings evidence to show that the obliquity 

 of the distal end of the quadrangle is not a direct heritage from the 

 Anisozygoptera, but rather by a parallelism or independent devel- 

 opment, and In general is a sign of specialization. 



I think that enough evidence has now accumulated to show that 

 this obliquity may in turn, grow less and the quadrangle be re- 

 stored to distal squareness. In other words, the quadrangle is not 

 as fixed and unchangeable a part of the wing as might at first be 

 supposed. How else can the same shape of the quadrangle be 

 explained in three widely separate groups which agree only in the 

 reduction of Cu2? I refer to Disparocypha (fig. 37), Lestoidea (fig. 

 45), and the Protoneurinae. Evidently when this reduction takes 

 place new demands for bracing must be met and the quadrangle 

 again becomes square. The squareness of the quadrangle, then, 

 in the lower Agrionidae and in the Protoneurinae, is no proof of a 



