1923] 
The Wing-Venation of Insects 
127 
that the latter is reunited at the base, which, from a morpho” 
logical standpoint, is of only relative importance; it is seen that 
Comstock’s and with the adventitious sector between, 
are Sm^ and Sm^; that Cu^ and Cu^, low nervures, with the 
adventitious sector between, are Scu^ and Scu^; that lA, high, 
isP; 2A, lowAsSp; 3A, high, isU. 
The high nervures M and Cu, which are present and simple 
in Triplosoba, are missing between Sr^ and Sm^, in some cases, 
between Sm^ and Scui in others; we may consider that they 
have disappeared, in consequence of the narrowing of the wing, 
a change which becomes very marked with the Protereismidse 
of the Permian.^ 
It is very interesting to show the Sm and its branches are 
high in the Ephemeroidea, while these nervures are low in Tri- 
plosoha, which brings back the regular alternation of high and 
low nervures broken up by the disappearance of the adjacent 
high nervures M and Cu. 
The wings of the Ephemeroidea differ from those of the 
Protephemeroidea by the reunion of the median with the sector 
of the radial near the base of the wing, by the disappearance of 
the anterior high median and cubital, the sub-median and 
sub-cubital alone remaining, the sub-median having become a 
high nervure. 
Following the conclusion of a work by Miss Morgan® 
Comstock agreed that in the Ephemeroidea the radial sector is 
represented by a small trachea arising from the radial, not far 
from the extremity of the wing; he considered as belonging to 
the sector of the radial the two final added sectors situated in the 
space which I have called sub-radial, and in which it makes a 
median space. These authors tried to discover in the wing of 
the Ephemeroidea the sector of the radial which they did not 
see, taking it for a branch of the median, and they sought the 
solution in a comparison with the wing of the Odonata. 
None of Miss Morgan’s drawings seem to me convincing; 
the numerous preparations of young larvae of Ephemeroidea of 
different genera Baetis, Cloeon, Leptophlehia, Ccenis) made at the 
Overmeire biological station by Mr. Paul Brien, student-assis- 
