Vol. 1.] Woodworth.—Wing Veins of Insects. 81 



almost, or quite, confined to the area increased or diminished. 

 Thus, if the two pairs of wings in ah aphid were cut across 

 just before they begin to become narrower toward the tip, they 

 would have an almost identical venation. In Hymenoptera 

 the front wing somewhat overhangs the hind wing. If the 

 front wing is cut across just before the beginning of tliis 

 extension and the hind wing also at the corresponding point 

 as indicated by the end of the first posterior vein, the venation 

 of the resulting basal portions will agree very closely in their 

 median area. The difference associated with the coordination, 

 since it affects the anterior and posterior areas only, constitutes 

 about all the difference there is. 



In a like manner the Psyllid*, the Psocidae, and other groups 

 show the truth of this general contention. The independence 

 of the different areas of the wings is further borne out by the 

 development of the sj^stem of plication veins in many of the 

 Elytroptera, as will be described when treating of those groups. 



There are three distinct regions of increase or decrease in 

 an insect's wing: the anterior, outer, and posterior margins. 

 The central area can be but little affected according to this law 

 of the independence of regions. Each of the three regions is 

 subject to different methods of vein increase or decrease. 



The anterior margin is limited at the base by the marginal 

 vein, which has become essential to the wing because of its 

 function of holding the wing spread. There can be, therefore, 

 little or no addition of veins at the base, though the margin 

 of the wing does sometimes extend out beyond the vein that 

 originally bounded it. The amount of increase of this area is 

 distinctly limited by the flight requirements, which hold the 

 primary near the front edge of the wing. In the cases where 

 the wing serves some other purpose than flight, as in certain 

 Phasmidae, this area may have enormous extension. The 

 added veins of this region always partake of the nature of 

 branches, though probably originating as independents, or pos- 

 sibly in some cases as cross veins. Whatever their origin, they 

 are soon indistinguishable from true branches. 



The diminution of added veins in the anterior region appears 

 to take place mostly from the base outwardly, but this is a 

 matter very difficult to decide. The svibject is one capable of 

 experimental study by decreasing by breeding methods the size 

 of insects that are subject to considerable variation in nature. 

 6— V 



