70 CLAUDE FULLER. 



In the stump of the fore wing the costa and post-costa seem 

 to arise from a common stem. The costa is, however, joined 

 by a bi'anch from the post-costa, see fig. 68 (PL VI), and the 

 costa, in a somewhat diminished form, extends around the 

 front margin of the stump. In the hind wing the costa suffers 

 a diminution at relatively the same point so that it enters the 

 wing-stump as a i-educed rib, and here, as in Hodotermes, 

 the post-costa is one of the chief ridges of the wing-stump. 

 Of all the hind wings examined, the post-costa fused with 

 the costa shortly after entering the lamina, fig. 86 (PI. VII), 

 with two exceptions. In these it Avas almost independent of 

 the costa in the lamina?, fig. 87 (PI. VII). In only one fore 

 wing Avas the post-costa found fused to the costa, and then so 

 that the tAvo formed a " double-barrelled " rib. 



The A^ariations of the A'enation can only be understood and 

 the abnormalities explained by a study of the deA'elopment and 

 behaviour of the pre-existing tracheae. Much of this has 

 already been alluded to at length in other sections. Attention 

 may here be draAvn to the development of the tracheal system 

 as illustrated by the series of camera lucida sketches rendered 

 as figs. 88 to 94 (PI. VII). The following points Avill be 

 noticed : (a) the constant presence of the post-costal trachea 

 in the hind Aving-sac ; (b) the building up of the main sj'stem, 

 fig. 93 ; (c) the secondary development of minor tracheae accom- 

 panied by the lengthening of the main series, fig. 94 ; and 

 (d) the " pot-bound" effect caused by the marginal thickening. 



Notice may also be taken of the A^aried development of the 

 anal or anals. Commonly there is a single simple anal present, 

 figs. 92 and 97 ; not infrequently the single anal is furcate, 

 figs. 94, 95 (PI. VII) ; rarely it is three-pronged, fig. 99a 

 (PI. VII). Quite often there are tAvo anals, and both may be 

 simple, figs. 93, 98a, or one may be simple and another 

 pronged, fig. 96. Inhabiting an atrophied part, the anal 

 is, in Avhatever form, atrophied; that, when displaced, it is 

 capable of considerable development is illustrated subse- 

 quently. 



In comparatively young nymphs one finds abnormal tracheal 



