No. 384.] THE WINGS OF INSECTS. 907 
In most Libellulidz a trachea, or a bunch of tracheoles, 
descends from near the base of the radial sector and forks at 
the level of the bridge, one branch going to the distal end of 
the oblique vein, the other going in a diametrically opposite 
direction to the media (Fig. 64). 
The illustrations just given exhibit the structure of these 
parts in nymphs of the suborder Anisoptera. In the suborder 
Zygoptera (Calopterygide and Agrionide) there exists a strik- 
Fic. 64.— The region of the nodus in Lidel/ula pulchella. o, oblique vein; 47, the bridge. 
ing difference. If we compare adult wings of the two sub- 
orders, there can be no question as to the identity of vein Ry 
or as to its homology in the two groups. But in the suborder 
Zygoptera, so far as known to us, the trachea R, is a branch of 
the medial trachea. The base of R„ however, forms an oblique 
vein, and a bridge is developed secondarily, as in the Anisoptera. 
It is probable that there has been a switching of the base of the 
trachea R, from trachea & to trachea M. One has only to 
examine a well-mounted wing of any dragon-fly nymph to see 
in the universal anastomoses of tracheoles communications 
already set up between principal trachez, any one of which 
