100 Annals Entomological Society of America [Vol. V, 
media. It soon splits into two branches which extend nearly 
to the anal margin. These branches are the Cu, trachea and 
the Cu, trachea. The Cu; trachea lies constantly within the 
vein directly behind vein M, and the Cur: trachea within the 
next primary vein. behind Cuy. 
A prominent bend in the cubital trunk is a characteristic 
feature of May-fly tracheation. Variations of it have been 
found in all but one (Pl. V, Fig. 5) of the wing-pads examined. 
(PI; V, Figs, GO sere Pl, Vis hiss. 1.5 al (el Vee ool eens 
the last case (Callibeetis) the-cubito-anal stem has joined the 
general approximation of the tracheal, trunks outward and the 
cubital bend is no longer evident. 
The replacement of main tracheze by small branches is not 
usual in the cubital region as it is in the radial and medial. It 
does occur however in Blasturus and Siphlurus (Pl. VI, Fig. 27; 
Pl. VII, Figs. 29,-40) where small branches of the.Cu, trachea 
supply the M3;+ vein. With few exceptions (PI. V, Figs\1, 3, 7) 
the cubital fag e are entirety unbranched. . 
The Anal Trachee. 
The anal stem is a well defined trachea which splits off from 
the cubito-anal trunk just before the cubital bend. 
In the mature wing-pad of.an Ephemera (PI. VI, Fig. 17) 
the three anal trachez are present. In this wing-pad the lst A 
trachea is a strong branch which separates from the distal part 
of the anal trunk and extends to the margin. It lies in the next 
primary vein posterior to vein Cup. From the posterior side 
of the 1st A trachea several secondary branches are given off. 
These are followed by secondary veins. The 2nd A trachea 
separates from the trunk directly behind the accessory trachee. 
The 8rd anal trachea is a short branch which arises posterior to 
these accessories. Both the 2nd A and 38rd A trachee are followed 
by primary veins (Pl. VI, Fig. 17). From the evidence pre- 
sented in the nymphal wing- pads and the wings of the sub- 
imago we have considered veins Ist, 2nd, and 38rd A to be 
typical of May-flies. 
In Chirotonetes (Pl. V, Fig. 1) I have been able to demon- 
strate but one anal trachea. In this and all the other genera 
examined the anal tracheze appear much later than those lying 
farther anterior. This fact accounts for their absence in many 
of these figures. The first anal trachea has been found in all of 
