Vol. 1.] 



Woodivorth. — Wing Veins of Insects. 



97 



were broad, so that there must be a large series of veins radiat- 

 ing from the second posterior, the strain on this vein wouhl 

 require the strengthening of the area in front of it, which could 

 be accomplished by the development of a cross vein along the 

 already existing ridge, extending from the second posterior to 

 the hind one of the two independents, or at least along the 

 outer (distal) half of this ridge. In time this vein would come 

 to look like the direct continuation of the first posterior, con- 

 necting it with the hindmost independent, as indicated by the 

 lower of the two dotted lines in Fig. 80. An area thus pro- 

 duced agrees in every particular with the condition of the 

 triangle. The second triangular cell resulting from the divi- 

 sion of this quadrilateral cell is always recognizable in front 

 of the triangle, and the cell marked s by Comstock and Need- 



FIG. 30. Portion of the 

 base of the wing of Archi- 

 lestes, showing probable 

 origin of triangle. 



FIG. 31. Venation of Protephenie- 

 ridte, with cross veins omitted. Dotted 

 lines are veins that are sometimes 

 wanting. 



ham (e. g., their Fig. 62) is thus shown to be bounded by the 

 two posteriors and the basal half of the newly formed diagonal 

 cross vein. 



PROTEPHEMERTDiE. 



The Paleozoic insects grouped under this family name pos- 

 sess four equally developed wings. Aside from this character, 

 and the structure of the thorax correlated with it, these 

 insects are not particularly different from the mayflies of the 

 present day. The unusually abundant development of the 

 posterior veins resembles the condition in Ephemerida?. There 

 seems to be nothing against the idea that we have in this group 

 an early equialar stage in the evolution of the modern group. 



The character of the venation is well indicated in Fig. 31, 

 in which all except the cross veins are shown. The latter are 

 very variable in number, rather regularly placed, and quite 

 uniform in size, therefore not particularly significant. In one 

 point, however, these early wings stand in contrast with those 

 of the modern group. It is the absence of free independents. 

 The production of free independents prior to connected ones 

 7— y 



