113 



insect wings there exists a type of branching which is very- 

 different from that of our hypothetical primitive type. An 

 examination of Figure 5, which represents the latter, will show 

 that in every case 

 the forked veins are 

 branched dichoto- 

 mously, while in the 

 many-veined wings 

 the more character- 

 istic type of branch- 

 ing results in the 

 formation of pecti- 

 nate veins; this 

 pectinate type of 

 branching is well 

 shown by the cubi- 

 tus in a cockroach 

 (Fig. 10 Cu). 



The changes that 

 take place in the 

 development of the 

 pectinate type of 

 venation from the 

 dichotomous type 

 are of two kinds : 

 first, the develop- 

 ment of accessory 

 veins ; second, the 

 modification of the 

 primitive veins so 

 that they are no 



longer dichotomously branched. The former has been dis- 

 cussed above ; we will now briefly refer to the latter. For 

 this purpose we will give a series of diagrams illustrating 



Fig. II. — Diagrams of several types of radius. 



