56 UniversiUj of California Puhlkations. [Entomology 



the wingpad shall everywhere develop alike. This seems 

 possible only when the corresponding areas lie strictly opposite 

 each other. 



It is not necessary that each individual cell be connected 

 with a corresponding cell on the other side, but only that 

 enough points of attachment exist to insure the general cor- 

 respondence of the areas, and, in larger wings, of the principal 

 folds. Mayer has pointed out the utility of these connectives 

 at the time of the ecdysis, but no one has suggested their evi- 

 dent primary function, that of correlating the position of the 

 cells in the wing membranes. 



The relation of the hairs and scales to these folds is very 

 evident, those of the membrane areas being at the peak of 

 somewhat conical elevations produced by the double folding 

 If the folds of the two sides of the wing exactly correspond, the 

 hairs or scales in the imago would exactly match. In some 

 insects this is true to a degree that is marvelous, scarcely a 

 single hair in the whole wing being without its mate, both 

 so perfectly placed that in focusing, the transition from one 

 set to the other may be easily overlooked. In other insects 

 there is no evidence of any relationship, showing that the 

 connection was of the most general kind. In Lepidoptera 

 there is usually a general conformity, but seldom a very strict 

 one. 



On the veins there is never the precise opposition of hairs 

 or scales that is sometimes seen on the membrane. However, 

 when they occur in rows, there are generally in a given 

 distance the same number on the two sides. This condition 

 corresponds with the entire absence of connection of the two 

 sides in the vein region and to the equality in the size and 

 number of the folds upon which the straightness of the vein 

 depends. 



The hairs or scales lie much closer together in the mem- 

 branous region of the wingpad than they do on the veins, for 

 the reason that the veins do not expand laterally at the time 

 of emergence, and this probably explains their differences in 

 structure, usually so evident. One of the functions of the 

 stronger hairs of the veins is doubtless to aid in the molting 

 process. Even in the case of Lepidoptera the vein scales, 

 though appearing much like the others, are very much stronger, 

 because of their thicker walls. 



