48 University of California Publications. [Entomology 



like those in that of the body walh A difference of intensity 

 can generally be recognized, often bringing these three regions 

 into very sharp contrast one with the other. Pigment may be 

 absent from any one of these regions, but some pigment is 

 always present, unless it be in the case of very small wings in 

 which the veins are presumably degenerating. 



The first region of pigmentation is the one usually seen as a 

 uniform tint over the vein surface. It is often more feeble 

 than in the other regions, but sometimes persists when that of 

 the others is not recognizable at all. This may be seen most 

 evidently in veins without lumina. Sometimes when the other 

 regions are well pigmented, it is evident only locally, as illus- 



\ 



FIG. 19. Portion of wing of 

 ,lp/.v, showing different kinds FIG. 20. Bulla in 



of pigmentation at bulla. wing of a wasp. 



trated in Fig. 19. A differentiation of the surface pigmentation 

 may be seen in the case of tracheoid veins where the surface 

 elevations are very much more densely colored than the inter- 

 vening hollows, thus bringing out the structure of the vein 

 very plainly. This may be seen in Fig. 16. 



The second and third regions mark the border of the vein 

 and are not always readily distinguishable from each other. 

 The former lies within the substance of the vein, while the 

 latter belongs to the wing membrane. Sometimes one is more 

 prominent, sometimes the other. Differences come out most 

 conspicuously in the bulla. The second region either stops 

 abruptly or narrows into a sharp, but pale line marking the 

 edge of the lumen, while the third shows a tendency to spread 

 out and follow the fold, as seen in Fig. 19, or narrows into a 

 line similar to that of the second region, as may be seen in 

 Fig. 20. 



