THE WINGS OF ODONATA 



233 



formed. Intercalary veins in this order do not end free as they com- 

 monly do in the Ephemerida. 



Excellent illustrations of the modification of what is obviously an inter- 

 calarj^ vein into one that appears to be an accessory vein can be seen by 

 comparing homologous veins in the fore and hind wings of Chalcopteryx 

 rutilans (Fig. 235), as was pointed out by Needham ('03). In this species 

 vein IMib of the hind wing is obviously an intercalary \'ein; but in the 

 front wing this vein appears to be a branch of vein M2. The same differ- 

 ence eixsts between veins IRg^ of the two wings; that of the fore wing 



Fig. 235. — Wings of Chalcopteryx rutilans. 



appearing to be a branch of vein M3, while that of the hind wing is but little 

 more closely connected with vein M3 than it is with vein Rg. 



The resemblance of the intercalary veins to accessory veins is even more 

 marked in the wings of nymphs of this order than in the perfected wings. 

 This is due to the fact that in the Odonata there has been developed a most 

 wonderful extension of the tracheation of the \vings; not only are the 

 principal veins traversed by trachea, but the}^ penetrate every cross-vein as 

 well. It is not strange, therefore, that branches of the principal tracheae 

 extend into the intercalary veins, giving them the appearance of accessory 

 veins. This is well-shown in the wings of a n\TTiph of Gcnnphus descriptus 

 (Plate V). 



The intercalar\' veins were tenncd interpolated sectors by Needham ('03), 

 the term sector being commonly used in the older terminologies for branches 



