﻿part 1J 



FROM THE BRITISH COAL MEASURES. 



47 



"to it in the direction of the wing-tip, the upper portion of which 

 it doubtless reached. 



The median and cubital veins present certain unusual 

 problems. In all Palseodictyopteroids, the median and cubital veins 

 ■each arise and continue outwards for some distance as a single 

 stem. The median shows least tendency to branch near its point 

 of origin, while frequently it continues as a single unbranched vein 

 for the greater part of its length. The cubitus in many Car- 

 boniferous insects often sends off a long anterior branch only a 

 little way out from the base, or early divides by forking. In 

 the present instance, three veins occupy the position of the normal 

 median and cubitus. Of these, two either arise from a common 

 root or so close together as to be indistinguishable, while the 

 third has an independent origin from the other two. Further, 

 the third of these three veins sends off, soon after its origin, 

 .a stout outwardly- and forwardly-directed twig, which joins the 

 second of the two anterior veins and merges with it. 



If we assume that the two veins, arising from a common 

 point, represent the median vein, which forks at the base of the 

 wing, the third of the three veins will be necessarily the cubitus, 

 sending a twig forward to join the posterior branch of the median. 

 In this case the ' cell ' enclosed by the hinder median, and its 

 forwardly-directed commissure, will be a ' median-cubital ' cell, 

 and not a ' cubital cell' as assumed by Mr. Benjamin Cooke. 



On the other hand, as the median vein in Palseodictyopteroids 

 shows little tendency to branch, while the cubitus shows a distinct 

 tendency to branch, we may consider the median vein in the wing- 

 fragment to be a simple vein, undivided throughout that portion 

 of its length which is preserved, and arising in close union with 

 an anterior branch of the cubitus. The cubitus then becomes a 

 double-stemmed structure, the two elements of which unite by a 

 powerful cross-vein in such a fashion as to enclose a basal ' cubital ' 

 cell. Notwithstanding the common point of origin of the first 

 two veins under consideration, the latter view seems the more 

 logical one. 



A third view is that the median divides at the base, and that 

 the anterior branch of the cubitus goes off forwards to join the 

 inner branch of the median, the latter beyond the junction being 

 therefore a medio-cubital structure. 



If these veins be considered from the last-mentioned point of view, 

 the median is a simple undivided vein in the wing-fragment. It 

 arises close to the radius and the anterior branch of the cubitus, 

 the three veins being crowded together for a short distance, beyond 

 which the median bends backwards from the radius, and passes 

 outwards in the direction of the tip of the wing, in an almost 

 straight line. It is separated from the undivided portion of the 

 radius and from the radial sector by an area the width of which is 

 twice that which separates the radius and sub-costa, or that which 

 separates the main stem of the radial sector from the radius. 



The anterior branch of the cubitus lies close to the median 



