706 Rosert MATHESON 
Winged viviparous female, second generation.— Length 1.6-1.8 mm.; 
width 0.72-0.80 mm.; cornicles 0.28-0.32 mm. long. (The cornicles 
vary somewhat in length, but the majority are 0.32 mm. long.) | 
The abdomen is green, occasionally tinged with yellow, with three or four 
dusky patches on each side in front of the cornicles; the head, the thorax 
above and below, the cornicles, the cauda, the genital plates, the tarsi, 
and the distal ends of the tibiae and the femora, are black or blackish; 
the prothorax is margined in front and behind with green; dusky to black 
dorsal median patches on the sixth, seventh, and eighth abdominal: seg- 
Fig. 115. coRNICLES OF VARIOUS FORMS 
A, Aphis pomi, winged female, second generation, B, A. avenae, spring migrant; C, A. sorbi, spring 
migrant; D, A. sorbi, apterous female on plantain; E, A. sorbi, fall migrant; F, A. avenae, fall migrant. 
All drawn to same scale 
ments are usually present. Lateral tubercles are present on the prothorax 
and on most of the abdominal segments. The eyes are a very dark red, 
usually appearing black, with a small posterior tubercle and with three 
ocelli appearing as yellow-tipped elevations. The antennae are 6-jointed; 
the basal two and the last two segments are dusky to blackish, the others 
yellowish (fig. 114, a). The cornicles are cylindrical, gradually tapering 
toward the distal end, with a small, well-defined flange (fig. 115, a). 
The third generation 
As is well known, all the summer generations of this plant louse consist 
of viviparous females, reproducing without the intervention of males. 
