1930 ] Wing Venation of the Odonata and Agnatha 271 
elusion is very daring and was prompted by the wish to 
find a full analogy. However, Morgan is wrong in sup- 
posing that by such an interpretation a full analogy with 
the dragon-flies is established, because RS of the may- 
flies is a concave vein and corresponds completely to a 
concave vein in the dragon-flies, i. e., to RS 3 ; but not to the 
convex vein, RS 4 , which almost always has the character 
of a “Schaltsector,” and which, according to the under- 
standing of the authors is a branch of R,, i. e., RS. To this 
vein there entirely corresponds in the may-flies another 
convex vein, also always inserted, which Morgan indicated 
as I and Comstock as IRS (intercalary). If one attaches 
importance to such exceptional cases of the entering 
tracheal trunks, then we lose any support of the theory 
of the establishment of homology of the veins. Accord- 
ing to the illustration of Morgan (PI. 5, fig. 7) in Epeorus 
humeralis, the vein 1 is supported in the distal part by 
one trachea from M 2 . Why in such a case should we 
not consider vein 1 (that is, RS 4 ) to be only the branch of 
M 2 (that is, RS 5 ) and its basal part as a bridge? In Blas- 
turus, according to the same author (PI. 6, fig. 27), the 
middle (interia) vein of the media is tracheated by one 
treachea which separates from RS 5 (=M 2 Morgan). Why 
not suppose that the crossing once existed here, and not 
consider that this vein is a branch of RS 5 , etc.? Such a 
supposition is not more unlikely than the one assumed 
by Morgan. 
I have already noted above the fundamental nature of 
the relationship between the tracheation and the character 
of the venation. Those veins which have lost the normal 
method of origin from- other veins and become “inserted 
sectors” that is, after weakening at the base, have lost 
the base itself, those veins have lost the normal mode of 
tracheation and acquired a secondary tracheation. Such 
veins are the convex branches and also some small sec- 
ondary, distal, concave branches. It is true that not 
everywhere the convex vein-branches changed into “in- 
serted sectors”; there are exceptions, though very seldom. 
Thus in Palingenia, RS 4 in the fore wings 14 originates nor- 
14 In the hind wing this vein is already a typical inserted sector. 
