THE GENERAL FEATURES OF WISGS 



77 



studies of the \vin<i;s of Odoiiata. But similar scries of gradations between 

 an irregular network of veins and regular transverse cross-veins can be 

 found in the wings of several of the more specialized Paleeodictyoptera, in 



Fig. 64.- 



-Win<^ of Aenigmatodes danielsi 

 (After Handlirsch). 



which order regular transverse cross-veins first aj^ijeared. The wing of 

 Aenigmatodes danielsi (Fig. 64) will serve as an illustration of this. The 

 wing of Eurythomopteryx antiqua (Fig. 9) is an illustration of a palseodic- 

 tyopterous insect in which regular trans\-erse cross-veins had been fully 

 attained. It is evident, however, that the specialization of the cross-vein 

 occurred independently in different families of this order; and obviously 

 no homology exists between the cross-veins of two groups in each of which 

 they have been developed independently. 



While there is no reason to believe that homologous cross-\'eins exist 

 throughout the insect series, in several of the orders, where the number 

 of the cross-veins has been greatlv reduced, there are several cross-veins in 



Fig. 65. — The hypothetical primitive type of wing-venation with the named 

 cross-veins added. 



each case that so closely resemble in position those found in the other orders 

 of insects with few-veined wings, that analogies if not homologies can be 

 traced; and it has been found desirable, in order to facilitate descriptive 

 work, to name these cross-veins. The orders in which the named cross- 



