252 
Psyche 
[September 
tion itself, at the same time constantly keeping in mind as 
much as possible the function of the venation, and changes 
which should appear in the phylogeny of the wing by the 
w r ork of the separate parts of the wing and the work of 
its veins. Only after such investigation is it possible to 
approach the study of the history of tracheation, which 
depends upon the venation and reflects its history. This 
I will discuss at the end of this paper. 
Let us first turn to the Palseodictyoptera. The “family” 
Dictyoneuridse has the most primitive venation (figs. 1 
and 2) ; the wings here are homonomous, hardly broadened 
at the base; sometimes their ends are somewhat pulled 
out and as if curved backwards (Stenodictya, Microdictya, 
Stilbocrocis, Polioptenus, et al). RS in the more primitive 
forms (Stenodictya, Microdictya) arises from R approxi- 
mately at the middle of the wing, or a little nearer to 
the base; but in the majority of other forms we encounter 
the process of its receding towards the base. Usually RS 
sends 3 or 4 branches posteriorly, not counting its con- 
tinuation; in some cases the second branch (counting from 
the base) does not reach the trunk RS, but adjoins to the 
first and sometimes ( Microdictya vaillanti, Stilbocrocis, 
Eumecoptera) forks dichotomously. The media is divided 
into two branches, which we shall call M. anterior (MA) 
and M. posterior (MP) 5 ; MA in this family, as well as 
in the majority of other Palseodictyoptera remains simple; 
MP branches in the Dictyoneuridse, often forming three 
branches (Stilbocrocis, Eumecoptera, Dictyoneurula, Acan- 
thodictyon, partly Polioptenus), in which it greatly reminds 
us of M in the Ephemerids. Normally the cubitus also di- 
vides not far from the base into two branches of which 
the first (anterior), CuA, usually remains simple as in 
Polioptenus and Eumecoptera (figs. 1 and 2) ; the posterior 
branch, CuP*, usually gives rise to smaller branches. 
In the very primitive forms the anal veins form a com- 
paratively homogeneous series of 3-4 veins, which gradu- 
5 The development and configuration of the media have just the 
same characteristics as R. MA corresponds to the radius proper (R) ; 
MP, to the radial sector. The same was originally true of the 
cubitus (Cu). 
* Misprinted MP in original. 
