710 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



striking- point. Its shape and extent vary considerably and are often 

 characteristic of groups; but the stig'ma seems not to contain in itself 

 such characters for the critical determination of the coui-se of speciali- 

 zation as are furnished by surrounding parts. 



In the wings of the more generalized members of several families:! 

 of Odoiiata there is ])etween veins i?i and J/j a series of cross veins, 

 several of which fall directlv under the stigma, and all of which are ( 

 nearly or quite perpendicular to the veins they connect. One of these (j 

 cross veins which happens to lie at the proximal end of the stigma; 

 waxes stronger than its feilow\s, and is set in an oblique position in suchi 

 way as to strongly brace the stigma against vein 31^. Three not 

 remotely related Gomphinfe will illustrate the stages in the develop- ^ 

 ment of this strong brace from an ordinary cross vein. In Ejngom-] 

 plim 2^aludo8us (fig. 8) the proximal end of the stigma has no cross ij 

 vein exactl^v in line with it; in Cydophylla d/phylla (Plate XXXIV, 

 fig. 1) it is in line, but little strengthened; but in Gom.pltus dilatatus 

 (Plate XXXIII, fig. 1) it has become a strong and evident brace. K\ 

 parallel series might be pointed out among the ^schninte (compare 

 such genera as StaurojMehia (Plate XXXIX, lig. 2), Basia^scJina 

 (Plate XXXVII, fig. 2), and Gynacantha (Plate XXXIX, fig. 3), and 

 the Agrioninfc offer another parallel, with the addition of an interest- 

 ing feature, which is illustrated by a series of such g-enera as Lestes 

 (Plate LIU, fig. 1), Philogenia (Plate LIU, fig. 4), Argia (Plate LIU, 

 fig. 5), and JSfeJudlennia (Plate LIV, fig. 8). In this series there is 

 the same development of a brace from a cross vein; and, correlated 

 therewith, a progressive angulation of vein M^ at the base of this 

 cross vein, forming a triradiate brace at that point. 



An entirely dift'erent method of bracing the front of the wing at the 

 stigma has prevailed in a few forms {Tliore, fig. 4, i', etc.). The cross 

 vein below vein li^ is not utilized, but the two veins bounding the 

 proximal and posterior sides of the stigma are deflected so as to meet 

 vein R^ in a strong Y-shaped brace, which, doubtless, serves a purposes 

 analogous to that served 1)}' the other triradiate l)race described above. 



Fig. -t shows at p the normal stigma of Anax jiniius, greatly, 

 enlarged. It shows, also, a few conmion forms of stigma, bothi 

 braced and unbraced (</ to t), and a few unconunon and more or less 

 degenerate forms {w to s), which will be discussed under another: 

 heading. 



THE REGION OF THE NODUS. 



Here at once we come upon very peculiar wing features. 



The nodus is the stout cross vein near the middle of the costal bor- 

 der of the wing, joining the costa, the subcosta, and the radius. It is 

 traversed by a more or less evident suture, making a flexible and 

 elastic joint which, without loss of strength in the parts which need 



