•52 CLAUDE FULLER. 



(a) The bulging outward of the spiracular (or cardinal) 

 trunk as in figs. 49, 55 (PI. VI). 



(&) Bud growth (radial, medial, and cubital), fig, 51. 



(c) Development of buds into tubercles, fig. 52. 



(d) Grrowth of the scape of the radial, medial, and cubital 

 tracheae, fig. 54. 



(e) Appearance of the bud of the post-costal, fig. 56. 

 (/) Development of post-costal. 



{g) Appearance of sub- costal, tig. 57. 



{h) Appearance of anal, fig. 58. 



(i) The elevation of the extended bow of the cardinal from 

 the horizontal to the perpendicular, fig. 60. 



The foregoing sequence of events applies to other species 

 having three basal attachments except that with some fi,f, 

 and h do not occur. It also applies to those species of which 

 the wing tracheas have only two basal connections except that 

 either no medial or no post-costal nor anal develops. 



The elevation of the bow of the cardinal, or the lifting of 

 the latter to the plane of the meso- and metanota, is necessi- 

 tated by the forming of a " shoulder " to the wing-sac. It is 

 accentuated by the downward "drag^' of the leg-tracheae 

 upon it (see fig. 60, PI. VI). 



Ordinarily, where there are three basal connections, that of 

 the medial is closer to that of the cubital than it is to that of 

 the radial, in young nymphs (fig. 52). An opposite state 

 of aifairs occurs subsequently and the base of the medial is 

 far removed from that of the cubital, sometimes to a very 

 great extent, figs. 203,205 (PI. XI). The change of position 

 is due to a considerable intercalary growth of the cardinal, 

 which occurs between the roots of these two tracheae. 

 Because of this secondary growth, the scape of the cubital 

 lengthens in proportion to the degree to which its attach- 

 ment is carried further and further from the mouth of the 

 wing-sac. 



A feature of much interest is the behaviour of the trachea 

 that enters the wing-sac behind the radial. This may be the 

 true medial or the pseudo-medial (outer cubital), but its 



