joo n 



xxxin, 22] 



NK\VS 



strong branch descending from .1/2, and then continuing the line of Rs 

 distad. If we compare this formation with that found in the larvae of 

 the Zygopterid family Lcstidae, we shall see plainly enough that O' is 

 the homologue of the oblique trachea in that family, and that the lonti 

 bridge of the Lcstidae is not the homologue of the bridge of Anisoptera, 

 but comprises all that part lying basad from O', along the line of the 

 so-called Rs. To the trachea which arises from M to form O' I have 

 already given the notation Ms, as well as to the vein that forms along 

 it in the imago, so that we may now continue to apply this notation in 

 the case of Uropctala. 



Text fig. i.Uropelala chiltoni Till., antepenultimate instar, forewing, region of 

 distal oblique vein, more highly magnified, (x 104.) 



In text-fig. 1 I have shown, very greatly enlarged, the condition of 

 the tracheation at the antepenultimate instar in the region of the origin 

 of Ms. The difference in calibre between Ms and Rs is exceedingly 

 marked. In the penultimate instar the calibre of Rs increases, while in the 

 last instar the calibres of Rs and Ms are approximately the same, 

 though Ms is usually still slightly the larger. In no case does Rs pro- 

 ceed beyond the position of the first descending cross-vein after O' ; 

 all the rest of the so-called Rs of Needham, together with the descend- 

 ing cross-veins and that portion of the radial supplement which carries 

 tracheae is supplied entirely from trachea 



We thus see that in Uropctala larvae, the single longitudinal 

 imaginal vein Rs of Xeedham is formed from three distinct 

 parts as follows : 



(a) A basal portion, arising from M3 near its origin, having no 

 precedent tracheation, and representing the bridge-rein of Needham in 

 the Anisoptera. 



(b) A middle portion, lying between O and O', which is preceded 

 by a trachea arising from R below the nodus, crossing Ml and M2, 

 running along O, underlying Rs between O and O', then touching .U.v 

 and finally turning off to supply the first cross-vein beyond O'. This 

 portion plus (a) represents the Ion;/ bridyc in the Lcstidae. 



