128 
Psyche 
June- August 
tant, have shown us nothing which recalls anything of the 
singular arrangement existing among the Odonata of the group 
Anisoptera. We have not seen the small sector trachea des- 
cribed by Miss Morgan; supposing that it really does exist, it 
has only the value of an adventitious trachea, the only value 
which can also be attributed to the famous trachea which, 
according to Comstock and Needham, represented the sector 
of the radial in the Odonata. 
Tillyard, to whom we are indebted for so many fine works 
on living and fossil insects, recently confirmed the opinion that 
the subnodal sector of de Selys-Longchamps among the Lib. 
ellulidse is the sector of the radial crossing the median nervure.^o 
I was for a long time persuaded that this nervure, absent in the 
Zygoptera, as Tillyard has shown is an additional simple 
nervure serving in the Anisoptera to close up the sub-radial 
space which was enlarged during the course of evolution; this 
nervure, which may be called the secant (S), is a physiological 
realization of what exists in the Neuroptera, where the enlarged 
sub-radial space is closed by a supplementary branch of the 
radial sector. 
Tillyard’s conclusion is that the neuration of the Odonata 
can be interpreted only by palaeontology. 
Here is the reply which I believe I can support, using as 
a basis what we have learned from the evolution of neuration 
in the Ephemeroidea, and what the evolution of the Odonatoptera 
shows us. 
In the Odonata, the nervures which all present-day ento- 
mologists consider as M^, M 2 , Ms and M^ are with me the four 
branches of the sector of the radial, Sr^, Si*2, Sr,^ Sr^, the sector 
of the radial being, as in the Ephemeroidea, reunited at the 
base of the median; the upper anterior median (iff) is represented 
alone by the high nervure at present designated by the symbol 
MS’ the posterior median (iSm) is absent; the anterior cubital 
iCu) has disappeared, as in the Ephemeroidea; the nervure 
considered as Cu^, low nervure, is the sector of the cubical 
(Scu); the nervure considered as Cu^, upper nervure, is the first 
anal or penultimate (P), reunited at the base of the sub-cubital, 
