THE PALEONTOLOGICAL DATA 



107 



tration of this is seen in Becquerelia Grehanti (Fig. 109), from the Upper 

 Upper Carboniferous of France. 



It is not necessary to multiply examples. It is evident from those given 

 above that the primitive cubitus was two-branched, and that probably 

 each of these branches bore a variable number of accessory vein, which had 

 no definite arrangement, as illustrated by Paolia vetusta (Fig. 106). From 

 this primitive type there were evolved the following: 



Forms in which the accessory veins of both branches of the cubitus 

 attained a definite arrangement, as in Stygne Roemeri (Fig. 107). 



Forms in which the accessory veins of vein Cui were lost, thus producing 

 the isolated front branch type, as in Eurythmopteryx antiqua (Fig. 108). 



Forms in which the accessory veins of vein Cu2 were lost, thus producing 

 the isolated hind branch type, as in Becquerelia Grehanti (Fig. 109). 



And finally, forms, not mentioned in the above discussion, in which the 

 accessory veins of both of the branches of cubitus were lost, producing a 



0<2 



Fig. log.— Becquerelia Grehanti (After Handlirsch). 



simple two branched cubitus. This t\-pe arose comparatively early and 

 was associated with very generalized features, as in the case in Steno- 

 dictya lohata (Fig. 77). It is this type that is most common among living 

 insects. 



The evolution of the anal veins. — The determination of the probable 

 primitive number and form of the anal veins in the wings of insects is a 

 more difficult matter than the determination of the probable number and 

 forms of the other principal veins. 



There can be no doubt as to the number of principal veins in the preanal 

 area. In the case of each of these veins, the trachea that precedes it, in 

 those orders where the tracheation is not reduced, arises separately from 

 the thoracic tracheae, and extends into the wing-bud for a considerable 

 distance before branching; thus fomiing a definite, distinct entity; and 

 in those orders where the tracheation is reduced the number and branching 

 of the principal veins of the preanal area is easily determined in the more 

 generalized forms. 



