36 A VENATIONAL STUDY OF THE ZYGOPTERA 



Mecistogaster (fig. 50), the higher Megapodagrioninae, and the 

 Coenagrioninae and Protoneurinae generally. I think fossil evi- 

 dence bears out this tendency equally well ; it is, as was said above, 

 apparently one dependent on reduction in the number of sectors. 



II. Matching up of the cross-veins in transverse series. — At the 

 same time that the preceding tendency becomes evident and, 

 largely in the same forms, it is very noticeable that the cross-veins 

 become matched up and form regular transverse series across the 

 wing. These are beautifully illustrated in the higher Pseudo- 

 stigmatinae, the Coenagrioninae and the Protoneurinae above all 

 others. 



Miscellaneous Features 



1. Differentiation of fore and hind wings. — This tendency so im- 

 portant among the Anisoptera has practically no place among the 

 Zygoptera. A marked difference in size and shape is noticeable in 

 only very few cases: Chalcopteryx (fig. 4) among the Polythorinae, 

 Pseudolestes (fig. 38) among the Lestinae, and sometimes Mecisto- 

 gaster (fig. 50) among the Pseudostigmatinae. These cases are 

 certainly evidence of a departure from the primitive condition. 



Many Zygoptera ha^T a fairly constant difference in the length 

 of the quadrangles of the fore and hind wings, enough so that one 

 can tell which is the front and which the hind wing. The Poly- 

 thorinae have this difference well developed in that the quadrangle 

 of the fore wing is much the shorter and with fewer cross-veins. 

 Among the Coenagrionidae several subfamilies have the upper side 

 of the quadrangle of the fore wing shorter than that of the hind 

 wing. But, generally speaking, the differentiation of fore and 

 hind wings among the Zygoptera is not of enough importance for 

 it to be considert^d a sign of specialization. 



2. The bracing of the stigma. — Dr. Needham has shown two ways 

 by which this may proceed, one by the cross-vein between Ri and 

 Ml below the inner end of the stigma becoming oblique and often 

 hypertrophied. This sort of bracing is not met with in the Agrioni- 

 dae, nor in the lower Lestinae nor Megapodagrioninae. In most 

 higher Lestinae, Megapodagrioninae, Coenagrioninae, and Pro- 

 toneurinae it is the usual thing. The plates in Handlirsch's 

 "Die fossilen Insecten" show bracing in Tarsoph/ehid, a genus 



