80 University of California Puhlications. [Entomology 



as connectives. If the independents are strong, and especially 

 if they are joined together basally, the necessity of the con- 

 nective cross veins being coijrdinated is by no means as 

 evident. On the other hand, if the cross veins are coor- 

 dinated and strong, there is no need of the independents 

 extending inwardly from the connecting cross vein, and they 

 may be entirely suppressed. 



There is a similar reason for the strengthening of the cross 

 veins into connectives to bind the primary to the front margin, 

 or to connect the first and second posteriors. The connective 

 between the primary and the front margin is of particular im- 

 portance, and is found in some form in the majority of insects. 

 This connective may not be so useful in directly preserving 

 the stiffness of the wing as it is for bearing much of the strain 

 consequent on the pull of the muscle that expands the wing. 



A matter that has a great influence on venation is the 

 uneven increase or decrease of wing areas. This subject has 

 never been adequately discussed, nor have I suflicient data at 

 hand to treat it in detail, and so can consider only the most 

 evident facts. The best evidence on this subject is that afforded 

 by the study of the front and hind wings of the same insect, 

 because we do not have to consider here the question of differ- 

 ence in type. Likewise, preference should be given to wings that 

 are as near alike in general appearance as may be. A very good 

 type with simple venation for this study is that of the Aphidae? 

 and a more complex one is that of the Hymenoptera. In both of 

 these cases there is a much simpler venation in the hind wing 

 than in the front, a difference not wholly explainable on the 

 theory of the reduced size, but apparently largely a matter of 

 difference in shape brought abovit by a change in the apical 

 part of the wing. 



In cases of this kind I think it is safe to assume that increase 

 in a wing area would do just the same things that a decrease 

 would undo. Where there is difference in size we need not 

 inquire whether one or both of these processes were in opera- 

 tion. In the cases suggested above we may suppose, to judge 

 by the number of veins in the most nearly related forms, that 

 the front wings are examples of increase and the hind wings of 

 decrease. 



The most evident fact brought out by an examination of 

 these wings (see Figs. 63 and 80) is, that the modification is 



