964 
Journal of Agricultural Research 
Vol. V, No. 21 
The lumen of this organ is occupied by a structureless yellow or orange- 
colored substance which extends by means of an elongated neck through 
an aperture in the chorion, thus opening upon the surface of the egg. 
Webster and Phillips state that the yellow matter appears like a liquid. 
In A. pomi and in A. avenae , in which the organ is also present, it has 
more the appearance of a wax. Certainly it has a definite form which 
it maintains even when the surrounding cells are removed from it. The 
material is not affected by alcohol, xylol, or chloroform. 
With the migration of the embryo to the surface and its revolution the 
cells of the polar organ are Withdrawn, leaving the yellow body unchanged 
in form and still attached to the chorion. In one specimen which was 
in the late stages of development the yellow body was found inclosed by 
the anal portion of the embryo. Usually, however, it appears never to 
come in contact with the embryo; and when the latter hatches, it is left 
behind in the eggshell. The writers have been unable to find anything 
resembling it in any of the newly emerged insects. 
Dorsal body. —With the resumption by the embryo of activities in 
the spring a change takes place in the cells of the polar organ. These 
flatten out, drawing away from the yellow mass as if the serosa were 
exerting an upward pull on them from all sides (PI. LXVIII, fig. 5). 
Through the migration of the embryo the amnion finally comes in con¬ 
tact with the serosa at a point where the latter joins the cells of the 
polar organ, and both amnion and serosa rupture at this point. 
As the embryo revolves, the serosa contracts until it lies as a thickened 
plate, the dorsal plate, near the anterior pole of the egg. In fact, in 
some cases the thickening takes place directly at the anterior pole, the 
plate moving later somewhat toward the posterior. During this con¬ 
traction of the serosa it draws the cells of the polar organ after it, so that 
when the dorsal plate is formed, these lie as an irregular mass just posterior 
to the serosal cells (PI. LXXI, fig. 2). 
After the formation of the dorsal plate has been accomplished, this 
body commences to invaginate at its center, forming a tube which 
extends into the yolk ventrad, inclining slightly toward the posterior. 
This tube is formed of both the serosal cells and those which formerly 
constituted the polar organ. These cells can not now be distinguished 
from one another (PL TXXII, fig. 1). 
This dorsal body soon separates itself entirely from the amnion and 
lies wholly immersed within the yolk in the form of a hollow sphere, one 
cell in thickness (PL TXXII, fig. 2). A little later this sphere breaks up 
and the cells disintegrate, probably being used as food by the embryo. 
Resting stage. —From the standpoint of life history the resting stage 
is one of the most interesting points in the embryology of this species. 
The embryo appears to be very seriously affected by changes of tern- ’ 
perature at this time, or rather by sudden changes to temperatures 
