162 ON THE WINQ-VENATION OF THE PLECTOPTEEA. 
Order, which will present, to some extent at any rate, the real lines of 
evolution ol: the Mayflies through the long period of time from the Lower 
Permian to the present day. That problem may well be left to a later paper. 
I also hope to continue the series already begun on the venation of Odonata, 
and to show how, in that Order, the behaviour of the radial sector has 
followed the lines set out in this paper for the Mayflies, though very high 
specialisations of the Odonate venation have masked the original close 
similarity between it and that of Mayflies. 
Oawthron Institute, Nelson, 
31 March, 1922. 
Literature Quoted. 
COMSTOCK, J. H., 1918.—'' The Wings of Insects.^' Ithacn, N.Y. (Chap. x.). 
CoMSTOCK, J. H., and Needham, J. G., 1899. — "The Wings of Insects:: 
chap. iv. contd." Amer. Nat. xsxiii, pp. 118-126. 
MoKGAN, Anna H., 1912. — "Homologies in the Wing- Veins of Mayflies." 
Ann. Ent. Soc. Amer. vol. ii. pp. 89-106, pis. 5-9. 
Needham, J. G-., 1903. — "A Genealogic Study of Dragonfly Wing- Venation." 
Proc. U.S. Nat. Mus. xxvi. pp. 703-761, 21 plates (No. 1331). 
Sellards, E.H.. 1907. — "Types of Permian Insects : Part II. Plectoptera.'^ 
Amer. Journ. Sci. xxiii. pp. 315-355. 
TiLLYARD, R. J., 1922. — "New Researches upon the Problem of the Wing- 
Venation of Odonata. I. A Study of the Tracheation in the Larval 
Wings in the genus Uropelala from New Zealand." Ent. News, xxxiii. 
Venational Notation used in the Text-figures. 
1 A, first analis ; lAj, IA3, its two branches. 2 A, second analis. 3 A,, 
third analis. C, costal vein or trachea, separate from the costal margin. 
Cu, cubitus. Cui, first cubitus ; Cuja, Cuji,, Cuic, its principal triad in 
Protereisma. Cu2, second cubitus or vena dividens. cu-a, cubito-anal trunk 
trachea, cxif, primary cubital fork. Imi, humeral brace, formed from the 
descending posterior branch of the costal vein. Ic, stump of Rs. M, media ; 
Mj, Mj, M3_,_4, the three branches of its triad. M5, its posterior branch, 
forming the upper arm of ihe cubito-median Y-vein, the lower arm being 
Cuj. Mj + Cui, in Protereisma, the main stem of the cubito-median Y-vein,. 
commonly called Cuj. mf, the primary median fork. Pc, precostal margin. 
R, radius ; Ri, its main stem or anterior branch. Rs, radial sector ; R2_,.3^ 
R4+,5, its two main branches ; further branchings are indicated, first by tlie 
four veins R2, R3, R4, Rr„ then by the suifixes a (anterior) or h (posterior) 
attached to any of these four veins, and finally by numerical prefixes 1 to 5, 
to avoid further suffixes. Sc, subcosta. sc-r, subcosto-radial trunk trachea^ 
in, tornus. 
