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. 



