THE WINGS OF ODONATA 231 



see in the universal anastomoses of tracheoles, communications already set 

 up between principal tracheae, any one of which might be enlarged, should 

 necessity arise for the entrance of air from a new quarter. Following this, 

 the atrophy of the old connection would complete the switching; which, we 

 believe is what has happened in the Zygoptera. It follows from this that, 

 so far as this portion of the wing is concerned, the Zygoptera depart more 

 widely from the primitive type than do the Anisoptera" (Comstock and 

 Needham '98). 



Plate VII, Fig. i represents a part of a left wing of a grown nymph of 

 Lestes rectangularis and shows the radial sector trachea attached to the 

 median trachea; but it also shows a developing vein in the typical position 

 of the subnodus. And in the wing of the adult (Fig. 232) the position of this 

 vein and its oblique direction, differing in this respect from the cross-veins 



Fig. 232. — Wing of Lestes rectangularis. 



between veins Ri and Mi clearly indicate that it is the subnodus. Evidently 

 this part of the radial sector has been presented although its trachea has 

 been lost. 



In his later work Dr. Needham ('03) points out several modifications 

 of this region of the wing in the Zygoptera. "Either the attachment of the 

 radial sector to media was made at three different places, or else, since its 

 reattachment, it has taken a different course in each of the three different 

 series within the suborder Zygoptera. In the Lestinse we find it separating 

 from vein M2 far beyond the subnodus, the point of its departure marked 

 by a more or less evident oblique vein, and a long bridge formed about 

 numerous approximated tracheoles and small tracheae, mainly derived from 

 neighboring branches of the media. In the Agrioninae (5. str.) it separates 

 from vein M1+2 near the nodus, and there is neither bridge nor oblique vein. 

 In Calopteryx it separates from vein Mi +2 far to the proximal side of the 

 nodus, and about in the more usual position of the proximal end of the 

 bridge; indicating that in this group at least a recurrent trachea, such as 

 precedes the bridge in the Aeschnidae, may have developed into the basal 

 attachment of the radial sector to media." 



In most Odonata the distal part of vein Rg lies between veins M-. and M3, 

 or in other words, only two branches of media have invaded the radial area 

 of the wing. But in the Australian Neosticta canescens ■ as figured by 

 Tillyard both trachea Mi +2 and M3 pass over the trachea Rj. 



