1912] Homologies in the Wing-veins of May-flies 103 
In the wing-pads figured in Pl. VIII, there is a gradual 
reduction of the main trachea in the front of the wing. This 
is shown first in Heptagenia (Pl. VIII, Fig. 45) where the base of 
the subcostal trachea has apparently fused with the radial trachea, 
liters by its total obliteration, (Pi VIII, Fig. 51). . In all of 
these except Callibeetis the Sc has been the only vein to dis- 
appear (Pl. VIII, Figs. 46, 48, 50, 54). Between M, and M, 
there are several accessory veins which are generally bent 
backward and attached to the vein next posterior. The direc- 
tion of their bending is just the opposite of these same accessories 
in the fore-wing. 
— Ses iwias 
ELLE 
Fig. 6. Hind wing of Palingenia longicauda Oliv. (After Eaton.) 
The direction and the attachment of these accessories was 
traced through a series of hind-wings. In a few of the gener- 
alized wings they were bent forward and attached to vein M, 
(Palingenia, Fig. 6) like the similar accessories of the fore-wing. 
Between this anterior attachment to M, and the posterior 
joining to Mz, figured in Heptagenia (Pl. VIII, Fig. 46) there 
were many intermediate positions. One of these is represented 
by Chirotonetes (Pl. VIII, Fig. 44). We may conclude then 
that the wing of Palingenia represents a generalized type of the 
hind wing in which a number of accessory veins are joined to 
M,; and M2 is a simple vein. This condition is very near to 
that in the fore-wing. By a general shifting backward the 
accessory veins have been thrown upon vein M,2 and have thus 
9 
made it secondarily a branched vein. There are 3 sizes of 
