82 University of California PuUications. [Entomology 



My own investigations have not gone far enough to show more 

 than this tentative conclusion. Still further decrease consists 

 in the suppression of the ends of the longitudinal veins. Either 

 the marginal vein may disappear, all except the extreme base, 

 as in many Lepidoptera, where the anterior vein has become 

 very important by taking part in the articulation; or the 

 anterior may weaken and fade out, as in Diptera, in which 

 case the marginal remains strong and only disappears by fus- 

 ing wdth the primary, the two melting together more and more 

 till only the bases are separate. 



The outer margin may increase by . elongation, or, by a 

 broadening, probably in all cases by growth in both of these 

 directions, though in different relative degrees. There is no 

 limit to the amount of extension, except the mechanical one 

 due to the necessity of support by the basal parts. If the 

 extension is chiefly longitudinal, the primary and the inde- 

 pendents are simply extended and strengthened and the latter 

 increased in number. If the extension is very great, they 

 assume an oblique position. On the other hand, if the exten- 

 sion is largely across the diameter of the wing, making a tri- 

 angular wing, the effect is greatly to increase the independents, 

 as in the Ephemeridse, to strikingly change their course, as in 

 the Psocidffi and Aphidse, or to favor the holding of a consid- 

 erable number of cross veins, as in the Hymenoptera. The 

 latter tendency we can consider the normal course, as in the 

 Ephemeridae there is as much increase in length as in breadth, 

 and in the other cases the small size of the wings prevents the 

 natural tendency from showing itself. The peculiarities of the 

 reduced wings in Hymenoptera indicate that in general the 

 diminution is by the suppression first of these cross veins, and 

 then of the longitudinals. 



The hind margin is expanded in the hind wing much more 

 commonly than in the front wing, though there are some cases 

 where evidence of this specialization may also be seen in the 

 front wing. Usually the front wing shows evident reduction. 

 The method of increase of veins is usually by the production 

 of additional posterior veins, and if there is a tendency in the 

 wings toward the production of numerous independent veins, 

 there may be one or more in each interspace. The character- 

 istic thing about this area, however, is the duplication of the 

 posteriors. This area can not be very greatly expanded with- 



