74 University of California PuUications. [Entomology 



venation is the arrested development of the veins of the poste- 

 rior region of the front wing as compared with the hind wing 

 when the latter has become somewhat expanded. 



The coordination of the two wings permits more variation in 

 shape than in non-coordinated wings. We find, therefore, in 

 these wings, much greater range of variation in venation. Coor- 

 dinated wings are not usually of the same size. When the front 

 wing is the larger, it is always longer than the hind wing; but 

 when the hind wing exceeds in area the front Aving, the differ- 

 ence is wholly in their greater width, except in certain beetles 

 and cockroaches. In making this generalization we are con- 

 sidering only cases where both wings are functional as organs 

 of flight. 



The simplest method of coordination is produced by the 

 development of the adjacent edges so that they overlap each 

 other, the hind wing always lying beneath the front wing. 

 The other method consists in the specialization of structures 

 on both wings, by which these organs are held firmly together. 

 When wings are bound together they act as a single wing, and 

 the mechanical needs of the different areas have but little in 

 common between corresponding parts of the two wings. This 

 gives ample reason for the differences that have been brought 

 about. 



The rule is that, if there is any difference in the number of 

 veins in the anterior or posterior areas, the lesser number will 

 occur in the posterior region of the front wing or in the ante- 

 rior region of the hind wing. A simple and very striking 

 illustration of this may be seen in the wings of the hone3'-bee 

 (Fig. 92). 



There is always a certain amount of disturbance of the vena- 

 tion in the region where the connecting structures are developed. 

 Both the character and the position of the veins may be modi- 

 fied in this region. The attachment may be accomplished by 

 means of a groove, produced by the folding over ventrad of a 

 portion of the hind edge of the front wing to the extent of 180 

 degrees, and the development, on the adjacent part of the hind 

 wing, of a series of hairs, much enlarged and specially modified 

 into hooks which fit into the groove above. This is the struc- 

 ture in the Hymenoptera. Another modification, occurring in 

 Cicada and related insects, differs in having a portion of the 

 front edge of the hind wing bent upward into a hook locking 



