XO. 12 FLYING APPARATUS OF P.LOW-FLY RITTER 21 



4. Processus pteralis alee 4 (pi. 8. fig. 24; pi. 9, figs. 25, 26; pi. 

 II, fig. 29; pt4). Before taking this processus into consideration 

 I shall describe the inner marginal vein of the lobulus, with which 

 it is closely connected. The deep incision which separates the lobulus 

 (text fig. 2; pi. 5, figs. 15, 17; pi. II, fig. 29, lo) from the wing 

 proper extends as far as the origin of the axillary vein. The prox- 

 imal part of this vein is a strongly chitinized thickening of the wing- 

 lamella, and connected with the anal vein. This thickening forms 

 at the same time the point of origin of an elevated (convex) fold 

 which extends to the tau of Lowne (1890-1895, vol. i, pi. 10, t) 

 and passes into it. The crest of the fold, together with the tau, 

 form the margin of the lobulus, and are together to be considered 

 as its inner marginal vein (pi. 11, fig. 29, ie). The proximal end 

 of this vein loosely articulates by means of a sort of ball and socket 

 joint with the posterior (anal) marginal thickening of the squamula 

 (see pi. II, fig. 29). This marginal thickening bends downward 

 and inward, and passes into the processus pteralis ala; 4, which is, 

 in truth, the proximal, terminal portion of the inner marginal vein 

 of the squamula. As the proximal end of this is strongly chitinized 

 and differentiated as an articulating part, I reckon it among the 

 processus pterales. The processus pterale alje 4 has a depression 

 into which fits the anal process of pterale A. The surface of the 

 terminal portion of the processus pterale alse 4 is in one place saddle- 

 shaped. This saddle fits, as already stated (see thoracic portion), 

 onto the saddle of the processus pterale thoracis II. Between the 

 remigium and the processus pterale alse 4 lies a stay (pi. 9, fig. 

 25? '^1) which occupies the entire space between these structures and 

 pterale B. It is especially well developed near the processus pterale 

 alse 4, where it is thickened to a disk. This stay is connected with 

 the remigium by a strip of chitin (pi. 9, fig. 25). The parts of 

 the joint are united by a chitinous membrane, and they can be con- 

 sidered as strong, local thickenings of this membrane. These artic- 

 ulating parts may well be considered as originating, so far as they 

 are independent of the veins, from stimulations acting on the cover- 

 ing membrane so as to induce them to increase in thickness locally. 

 The uniting membrane is flexible, but of considerable tensile 

 strength. 



The foramina prajalaris and postalaris are bridged over by loose 

 ligaments: the ligamenta praealare and postalare. 



