Feb. ai, 19x6 
Green Apple Aphis 
963 
It is thus carried to the interior of the egg with the developing germ band 
(PI. LXIX, fig. 1). As the embryo develops, the ovarian yolk re¬ 
mains in connection with its posterior extremity, enlarges, and when this 
extremity becomes recurved, the yolk may be seen as a large, somewhat 
dumb-bell-shaped mass lying within the curve. At this time the large, 
deeply staining cells which form the end chambers of the ovaries are dis¬ 
tinctly visible at its extremities. The remainder is a finely granular 
mass very similar in texture to that of the original ovarian yolk (PL 
LXIX, fig. 2). At a slightly later period the mass of the ovarian yolk 
becomes somewhat more enlarged in the heads of the dumb-bell at the 
expense of the “grip,” and the end chambers are already forming (PI. 
LXX, fig. 1). After the revolution of the embryo, the two heads of 
the dumb-bell-shaped yolk become separated, and it is henceforth rep¬ 
resented by two large, slightly elongated masses, one on either side of the 
ventral portion of the body, the end chambers distinctly formed, and those 
on each side connected with one granular body of this ovarian yolk 
(PL LXX, fig. 2). In embryos almost ready to hatch, these two large 
granular bodies are still present, although more elongate than in the 
earlier stages. Some of the first egg chambers are now formed, and eggs 
may be noted within. The remainder of the reproductive organs are not 
yet developed (Pl. LXXI, fig. 1). 
In the first instar of the stem mother these elongate granular bodies 
are still present. Webster and Phillips (17, p. 99) state that a group of 
cells which ultimately give rise to the generative organs separate off 
from the mesoderm during their “stage 6.” The results of the present 
writers do not uphold this view. It seems more probable that these cells 
develop in the ovarian yolk, possibly from migrants, in the very early 
stages of growth, and that they are carried to the interior with this yolk 
at the time of invagination; that they here form two groups, one on 
either side of the ovarian yolk, which ultimately divides; and that these 
two masses of the ovarian yolk remain throughout embryonic develop¬ 
ment and assist in the formation of the reproductive system. 
Polar organ. —Upon invagination the germ band leaves behind it, 
at the posterior pole of the egg, a group of large nucleated cells. This 
cell group has been recorded by Webster and Phillips (17, p. 98) as 
Occurring in Toxoptera graminum , and was designated in their paper as 
the “polar organ.” The writers have been unable to find any other 
reference in literature to the occurrence of such a body, either in the 
eggs of Aphididae or in those of any other insects. 
The writers have not observed the genesis of this organ, but by the time 
the embryo has attained its “resting stage” it consists of a single layer 
of elongate cells surrounding a pear-shaped lumen (Pl. LXVIII, fig. 4). 
A large nucleus is present in the outer portion of each cell. 
