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Psyche 
[September 
M 2 and M 3 ; treachese which go into these latter veins and 
into M 4 of the authors, join at the base into one common 
trunk, which enters the wing independently. Hence the 
conclusion that this trunk is M, that RS crosses Mi and 
M 2 , that the bridge is a secondary formation, that the 
cubitus is two-branched, etc. Among the may-flies Com- 
stock discovered at first a type of tracheation very dif- 
ferent from that of the dragon-flies, and nearer to the 
normal. From this tracheation Comstock was led to an 
interpretation essentially similar (if not in names) to the 
one of Eaton (5) and other authors. Ann Morgan (8) 
undertook a careful investigation of the tracheation of dif- 
ferent species of may-fly nymphs and discovered that the 
tracheal stem which sends small tracheae into the branches 
of Comstock's RS usually arises independently from the 
common tracheal wing stem. Consequently, she concluded 
that the system of veins which include these tracheae do 
not represent RS, but M, as in the Odonata. Usually in 
the may-flies the trachea RS does not arise from the 
trachea R, as it does in dragon-flies; but in one species of 
Heptagenia, and even then only in part of this specimen, 
Morgan succeeded in finding a weak trachea which led off 
from R, crossed M and entered into the region between 
Mi and M 2 . Following the ontogenetic method of Corn- 
stock, Morgan concluded that the may-flies also originally 
had the radial sector cross the media. 
Comstock, in his later work on the wings of insects (3), 
which represents an enlarged and somewhat changed edi- 
tion of the joint work of Comstock and Needham (4), 
agreed with the results of Morgan and accepted, therefore, 
her interpretation of the wing venation of may-flies. By 
this interpretation the venation of the may-flies was brought 
(to a certain degree) up to the scheme 2 of the venation 
of the dragon-flies; but by the same interpretation the 
Ephemerid venation appeared to be extremely remote from 
that of the Palseodictyoptera and even the Carboniferous 
Triplosobidse Handl. Although the latter are placed in 
2 Only to a certain degree, because Rs of the may-flies in Morgan’s 
paper is not this vein in the dragon-flies. In the latter Rs (of author’s) 
corresponds to our Rs t , and R 5 (Morgan and Comstock) of the may- 
flies corresponds to our Rs 3 . 
