40 TJniversitij of California Publications. [Entomologt 



PART II.— VEINS AND VENATION. 



VEIN STRUCTURE. 



Before it is possible accurately to discuss the problems of 

 venation, it will be necessary to inquire into the nature of a 

 vein, in order to determine whether we have to. deal with a 

 single type of structure or with a number of fundamentally 

 distinct, though superficially similar, organs. The majority of 

 authors have accepted one or the other of these views, without, 

 however, discussing the question. As a consequence they are 

 often inconsistent, and in most cases have evidently given the 

 subject very slight consideration. The points upon which 

 differences of opinion have b^een expressed are as follows: 



1st. It has been repeatedly maintained that such structures 

 as occur toward the tip of the wing of a beetle are not veins, 

 because they possess no lumen. 



2d. Most of the authors treating of the wings in Neuroptera, 

 Orthoptera, and, to a less extent, in other orders, have made a 

 clear distinction between veins and cross veins, not classing 

 them in the same category, chiefly because of the variableness 

 exhibited by the latter. 



3d. A difference is often m.ade between cross veins; certain 

 ones that are very constant in position are supposed to be 

 somewhat different in kind or origin from the ordinary and 

 more variable ones. 



4tli. In a few groups where long veins are numerous, most 

 ■ of those that are variable are supposed to be different in kind 

 from those that are more constant. 



5th. Very generally veins tliat arise from the base are con- 

 sidered as distinctly different from those without evident 

 basal connections. 



6th. Veins appearing as branches of another vein are often 

 treated as of a different kind from those whose inner end is 

 free or connected by only a cross vein with principal vein. 



7th. The vein that lies along the margin is often distin- 

 guished from the other veins, sometimes by evident difference in 

 structure, sometimes because of its position, especially when it 



