100 ENTOMOLOGICAL NEWS [xxxii, '21 



very faint, although one is still able to trace their course in 

 the wing. 



In comparing the Embiid shown in Fig. 7 with the Zorap- 

 teron shown in Fig. 5, the following points of resemblance 

 may be noted. The cross veins between Cnl and Cu2 have 

 been lost (although some of them were still retained in the 

 Embiid shown in Fig. 9), and the vein M is apparently un- 

 branched. The cross vein m-cu of Fig. 5 is not present in 

 Fig. 7, but its homologue occurs in the Embiid shown in Fig. 

 9. Vein Rs has only two branches in Fig. 7, while the reduc- 

 tion is carried still further in- Fig. 5, in which Rs is unbranched ; 

 and in both insects, there is a tendency for Rs (or its branch 

 R2+3) to approach Rl. Vein Sc has begun to fade out in 

 Fig. 7, and it is not visible in Fig. 5, although it may have 

 united with radius or costa in the latter insect. In Fig. 7 

 there is exhibited a tendency for the veins Rs and M to extend 

 parallel to each other down the central portion of the wing, 

 and this tendency reappears in the insects shown in Figs. 2 

 and 1. 



The Zorapteron type of wing (Fig. 5) approaches the Psocid 

 type shown in Fig. 8, and it is also suggestive of other more 

 highly modified types such as those shown in Figs. 3 and 4. 

 On the other hand, the Psocid type of wing (Fig. 8) is also 

 approached by that of certain Neuroptera (Fig. 10), which 

 apparently originated from a type very like that of the Plecop- 

 teron shown in Fig. 1.2. Thus, the two branched condition of 

 M and of Rs occurs in all three insects shown in Figs. 12, 

 10 and 8; and the character of the anals is quite similar in the 

 three insects under consideration. From these and other fea- 

 tures of resemblance, it is evident that collateral branches may 

 preserve certain structures in an intermediate condition much 

 better than is done by the more direct lines of descent, as far 

 as these particular features are concerned, and on this account 

 it is frequently almost as instructive to study the collateral 

 lines as the more direct ones, if one wishes to trace the evo- 

 lution of all of the features of an insect's body, or all of the 

 modifications met with throughout an order of insects. Fur- 

 thermore, the evidence furnished by a study of the venation 



