THE TRACHEATION OF WINGS 



19 



that we have named, can not be identified ; one of the oldest of these wings 

 is that of Eitrythmopteryx (Fig. g), which is also discussed in Chapter IV. 



''^ '^ 



Oil 1 



Fig. 9. — Wing of Eurythmoptcryx (After Handlirsch). 



In the course of the evolution of the few-veined type of wing nearly all 

 of the cross- veins were lost ; but five or six were retained and are still pre- 

 served in several orders of insects. These we have named as follows : the 

 humeral cross-vein (Fig. 10 h)\ the radial cross-vein (Fig. 10, r); the 

 sectorial cross-vein (Fig. 10, s); the radio-medial cross-vein (Fig. 10, r-m)\ 

 the medio-cubital cross-vein (Fig. 10, m-cii); the medial cross-vein (Fig. 

 ID, m)\ and the posterior arculus (Fig. 11, p. a.) The cross-veins are 

 described more fully in the next chapter. 



The tracheation of the wings of larvae and pupae. — The development of 

 the tracheation of the wings in insects with a complete metamorphosis, 

 where the wings reach an advanced stage of development within the body, 

 differs remarkably from that of the wnngs of insects with a gradual or with 

 an incomplete metamorphose. With the latter the wings of the njTnphs 



Fig. 10. — The hypothetical primitive type of wing venation with the named 

 cross-veins added. 



are developed as outward projecting appendages of the body, into which 

 the tracheae penetrate early; and there is a gradual, direct development of 

 the tracheation in the successive stadia. But in insects with a complete 



