1930 ] Wing Venation of the Odonata and Agnatha 253 
ally grow smaller nearer to the base ; but the more special- 
ized Ai is better developed, and others lose their indepen- 
dence, uniting either with A 2 or even together with A x . 
There is no need to discuss the other families, because 
their wings were already specialized in different directions 
from those in which the dragon-flies and Ephemerids are 
specialized. 
All recent Agnatha differ sharply from the Palseodicty- 
optera, in that their fore wings are greatly enlarged at 
the expense of the hind pair (fig. 4), which have become 
completely reduced in many species (in sub-group Bsetoidea 
Ulm.). If the hind wings are present, the fore wings 
are wide and approximate a triangle ; then, where the hind 
wings tend to disappear, the fore wings take the shape in 
the first group (Ephemeroidea and Heptagenioidea) , which 
corresponds more to the shape of the fore and hind wings 
taken together. 
If the hind wings of contemporary Ephemerids differ 
greatly from the fore wings, this was not the case in the 
past. In the Ephemerids of the Permian the hind wings 
differed very little or not at all from the fore pair, and 
their form resembled very much that of the wings of Dic- 
tyoneuridse (13). Likewise, the wings of the remarkable 
Carboniferous Ephemerid Triplosoba Brogn. were homo- 
nomous (fig. 3). Handlirsch placed (6) this form into a 
special order, Protephemeroidea, because it preserved in its 
venation the features of the Palaeodictyoptera, particularly 
of the Dictyoneuridse. Just as in Eumecoptera (fig. 2) 
and in many other Dictyoneuridse, RS arises nearer to the 
base and sends posteriorly the usual four branches, of 
which (and this is very important) the second branch, i. e. 
RS 4 , originates near RS 5 , and RS 3 and RS 2 , together with 
RS 1 , form the distal group. Evidently RS 2 , already form- 
ing the “inserted sector,” did not reach RS 4 . M, as in 
the Dictyoneuridse, is divided near the base into the same 
two branches, MA and MP ; MA also, as in the Dicty- 
oneuridse, remains simple, while MP is divided distally into 
three branches, the middle one and the two supplementary 
ones beside it being already changed into “inserted sectors” 
(Schaltsectoren) . The close similarity of this MP with 
M in the real Ephemerids leads us to believe that M of 
