226 



THE WINGS OF ODONATA 



in front of trachea Rg. The costal trachea is greatly reduced or, rather, 

 outstripped by its competitors; the same is true in a less degree of the 

 subcostal and anal trachea. At this stage the veins, which are not repre- 

 sented in this figure, appear as pale brownish thickenings; surrounding all 

 of the principal tracheae, and also surrounding the small tracheae and anas- 

 tomosing tracheoles, which tend to group themselves in the positions of the 

 cross- veins. 



Plate V is a reproduction of a photograph of the wings of a grown 

 nymph of Gomphus descriptiis in which both the tracheae and the forming 

 wing-veins can be seen. A comparison of this figure with Figure 229, which 



Fig. 228. — Tracheation of the wings of a grown nymph of Gomphus descriptus 



(After Needham '03). In the specimen figured the first branch of the 



anal vein of the fore wing was switched to vein Cu. In the 



hind wing this branch was normah 



represents the wings of the adult, and also with the two preceding figures 

 (Figs. 227 and 228) will enable the reader to see the correctness of the 

 conclusions regarding the homologies of the wing-veins, which are indicated 

 by the lettering of Figure 229 and Figure 230. See also Plate IV, 

 Fig. I. 



An important factor in the strengthening of the wings of the Odonata 

 is the development of a series of corrugations. This has resulted in certain 

 veins becoming convex and others concave; that is the wings are of the 

 spread fan-like type. In fact the wings of the Odonata are the most perfect 

 examples of this type known. 



