}o.l331. 



DRAGON-FLY WING VENATION— NEEDHAM. 



707 



been modilied to produce the Odonate type, in which the most anom- 

 lou.s thing is the crossing of the radial >!ector over two hranchcs of 

 he media. I can not now suggest even a possi])lc reason why this 

 jhould have taken place. It is apparently a character (luite dis- 

 inctive of the order Odonata. 



■ A photograph of fore and hind wings of a grown nymph of the 

 iame species, showing the tracheae and the veins together as they 

 Ippear during the last nymphal stage, is reproduced in Plate XXXI, 

 fio-. 1. This will assist greatly in comparing the adult wings shown in 

 4g. 3 with the preceding figures. This also shows that certain well- 

 Snown features of the dragon-fly wing are due to strong cuticularisation 



Fig. 2— Fore and hind wings of a grown nymph of Gomphus descriptus, showing trache.*-. 

 The permanent venation which shows distinctly at this stage is omitted. 



between the tracheae. Such are the stigma (sf.), the nodus (>^), and 

 parts of the arculus (ar.) and triangle (f.). 



The radial sector.— In the adult wing (fig. 3) the radial sector appears 

 to be a branch of the media. It has always been so interpreted. The 

 only indication of its connection with the radius is the persistent 

 obliquity of an apparent cross vein between veins J/., and Rs. This 

 is in fact not a cross vein, but a part of the radial sector, while the 

 longitudinal trunk (hr.) extending proximally from this point to (^on- 

 nect vein lis with vein J/i+/' is not homoloa-ous with any principal 

 vein, but is a secondary structure developed for mechanical advantage. 

 There will be seen in the plate a recurrent tracheal twig preceding this 

 structure. 



«The plus sign is thus used as a convention for indicating united branches or 

 tracheje, the numerals it connects designating the branches conjoined. 

 Proc. N. M. vol. xxvi— 02 48 



