Four brachypterous males were taken at Ribbonwood Creek in February, 1932, associated with a normal winged female. Tillyard (1926) states that brachypterous males occur in other genera associated with females. These insects are of the same size and resemble the normal imagines in every respect, except that the wings are only one quarter of the normal size. The body is pubescent, and the gut as in normal insects is filled with a gas, both evidently being adaptations correlated with reproduction, and with the fact that these insects are never far from water, so that such adaptations would prevent drowning.
At first it was thought that they might be of a different species, but a careful examination has revealed no grounds for regarding them as such. On the contrary, it is contended that they are brachy-pterous males of Stenoperla prasina, supported by the fact that external and internal anatomy conform to the same general plan as found in the nymph and other imagines, and that the external genitalia show no difference whatsoever from the normal male. Moreover, these males were sexually mature and endeavoured to copulate with the female, which, however, very unfortunately died, together with two males, during a very severe frost. Where possible a comparison of their internal anatomy was made with that of normal imagines, and was found to be identical.
The wings (Pl. 42, Fig. 40) are one-quarter of the normal size and lie flat on the terga of their segments, the forewings slightly overlapping the hind; the anal fan of the latter is doubled under the rest of the wing so that its dorsal surface lies ventrally on the tergum. It is slightly shorter than the fore. Both are the same colour, the wings of three specimens are olive green, whilst those of a fourth are purple in colour. When the insect is disturbed, no attempt is made to use these, but escape is effected by their very rapid running. The anterior margin of both is thickened around to the apex, and both are clothed with microtrichia. The venation is extremely variable, the wings of a single individual showing great variations.
The Forewing.—In the forewing C is absent unless the anterior thickening of the wing can be regarded as such, whilst Sc is two-branched as in the normal wing. The humeral veinlet is constant in position, and a variable number of costal veinlets pass from Sc across the costal space. Sc2 in all cases curves downwards and is fused with R1 for a short distance. R + M pass outwards some distance and then bifurcates into R and M. It is here that the greatest variation takes place. In the more typical forms R continues towards the margin for a short distance, and then divides into R1 and Rs; the former is a straight, unbranched vein terminating just anterior to the apex. Rs bifurcates distally into R2 + 3 and R4 + 5, but in some cases is undivided and passes out as Rs to the wing margin. M divides distally into M1 + 2 and M3 + 4, but M1 + 2 may or may not be fused at its distal extremity with R4 + 5. Cu runs some distance along the wing membrane and then splits into Cu1 and Cu2 (both of which are usually unbranched). A strong set of cross-veins in all cases is developed between Cu1 and Cu2. 1A is straight and unbranched, whilst 2A is two-branched.
The Hindwing.—The hindwing is lacking in C, and Sc is twobranched, Sc2 fusing with R1 as before. The humeral veinlet is constant, and there are a variable number of veinlets across the
costal space, usually three. There is a large space between the former and the latter. R + M passes out beyond the humeral, where it splits into R1 and Rs + M. Again, R and M show the greatest variation. Rs + M bifurcates into Rs and M, the former dividing into R2 + 3 and R4 + 5, whilst R4 + 5 in one specimen is branched into R4 and R5. M, however, may not branch, in which case it passes as such straight to the wing margin. Shortly after leaving R + M, Rs + M divides into Rs and M. Distally M bifurcates into M1 + 2 and M3 + 4, the former of which may or may not be fused with R4 + 5; the latter when present is always fused distally with Cu1 Cu divides into Cu1 and Cu2, the former fusing with M3 + 4 when present. 1A is a straight, unbranched vein, whilst 2A is two-branched. 3A has a variable number of accessory veins which increase the anal area. Nowhere on the hindwing can there be said to be a strong development of cross-veins, which occur irregularly over the whole wing membrane, and are very variable. The humeral is constant.