Vol. 1.] 



Woo<lu'0)i]i. — Wing Veins of hisects. 



115 



FIG. .54. Diagram showing intermediate forms between 

 the normiil hind wing and tliat of Diploptera, showing the 

 evolution of the plicated tip. 



There is another specialization in the hind wings of certain 

 cockroaches that is interesting, since it shows in an unmistak- 

 able way the formation of new veins in a folded area, and 

 because it gives us a hint of the way in which the Forficulid 

 wing must have been produced. This matter was first worked 

 out by Saussure ('68) in the manner indicated on the accom- 

 panying diagram (Fig. 54). In the evolution of Diploptera, 

 the wing is sup- 

 posed to have 

 success i ve ly 

 passed through 

 a series of stages 

 similar to the 

 conditions 

 shown in the 

 series of genera 

 illustrated in 

 Fig. 54. In this 

 way the whole 

 of the folded tip of the wing is shown to have come from an 

 increase in size of the minute triangular bit of membrane 

 occupying the angle of the principal fold. In none of these 

 forms is the plicated area at the tip provided with veins, except 

 the extreme member of the series (Diploptera), where they 

 must have been produced simultaneously over the whole area, 

 just as the reticulations of cross veins are. 



The lenticular anal field of the front wings of Blattidae, 

 which was already well developed in the Pala?oblattidae, is 

 clearly comparable with the anal area of all orthopterous and 

 hemipterous insects, and is also clearly homologous to the 

 folded anal area of the hind wings. This anal field is always 

 very distinctly marked off from the rest of the wing by a line 

 that is usually very much thinned and often quite transparent. 

 Another line of the same character is to be seen just behind 

 the primary vein. Between these two lines the area is occupied 

 by independent veins, usually clearly distinguishable as forming 

 three groups. The third of these is often specialized so as to 

 resemble a reverse of the many-branched primary. Because 

 of this peculiarity this vein has been identified as vein VII by 

 Redtenbacher and by Comstock and Needham, but the inter- 

 pretation of Brauer seems to be more sound and to accord 



