92 Annals Entomological Society of America [Vol. V, 
The most generalized tracheation which has been found in 
May-flies is represented in young stages of the wing-pads of 
Chirotonetes (Pl. VII, Figs. 33, 34, 35). From these and other 
generalized wing-pads (especially Pl. V, Figs, 5, 7) the accom- 
panying diagram has been drawn (Fig. 1). The treacheal 
system of May-flies arises at one point in the longitudinal 
trachea of the thorax and enters the wing base by a single stem. 
Near that area which is to be the base of the adult wing the 
entering stem divides into two trunks. These two trunks 
remain undivided but a short distance. 
Fig. 1. Tracheation of hypothetical May-fly wing-pad. 
The anterior trunk divides into two branches of unequal 
size. The smaller branch is a delicate trachea which extends for- 
ward, and outward parallel with the margin of the wing-pad. 
This is the costal trachea, (Fig.1C). Thelarger branch divides 
close to its base into two tracheze which extend nearly to the 
margin of the wing-pad. The anterior of these two trachez is 
the sub-costal (Fig. 1, Sc) and the posterior one the radial 
trachea, (Figs Ie). 
The foremost branch of the posterior trunk is the medial 
trachea, (Fig. 1, M). Beyond the point of its separation it 
divides into four branches. This agrees well with the condition 
of this vein in insects generally. The posterior branch bends 
toward the anal margin of the wing-pad. From its basal part . 
three separate branches are given off. These are the Ist, the 
2nd and the 3rd anal trachee. (Fig. 1, Ist A, 2nd A, 38rd A). 
A little beyond the lst anal branch the trachea splits into 
the two prominent cubital trachee. (Fig. 1, Cui, and Cuz). 
