102 
appear to be a greater number of cells about this body at this time. 
There is no trace of the dense yellowish center of the polar organ, 
otherwise it resembles this body very closely. However, as we have 
lost track of this organ in the gap between figures 1 and 2, and on 
account of the close resemblance between it and the dorsal organ 
of other insects, we have designated it as the latter. At a later 
stage (PI. VII, fig. 3) the dorsal organ has assumed a more nearly 
circular shape, the mouth having almost closed, inclosing a some- 
what pear-shaped space. At a still later stage (fig. 4) the dorsal 
organ has released itself from the margin, migrated backward, and 
"Begun to disintegrate. At length it disappears by absorption in 
the body cavity. 
At first we were not able to note a revolution of the embryo, but 
later studies show that such a revolution does occur between figures 
1 and 2 of Plate VII. 
After the ninth stage the development goes on very rapidly, and 
by the latter part of March the eggs are ready to hatch. 
During the fall of 1909 a number of eggs were collected that had 
been deposited in October and November, and these were kept until 
the spring of 1910 to note the time of hatching. Xo heavy freezes 
occurred until the 3d of December. It was found that although 
there was nearly a month's difference in dates of deposition there was 
not more than four or five days' difference in the time of hatching. 
An average of 64 per cent of the eggs hatched. We have also learned 
that eggs will not hatch unless subjected to freezing temperatures. 
SUMMARY OF EMBRYOLOGICAL DEVELOPMENT. 
There is a large almost circular mass of ovarian yolk at the poste- 
rior pole of the egg. 
Development begins almost immediately after oviposition, and 
proceeds more rapidly in the region of the anterior pole until after 
the blastoderm forms, after which growth almost ceases in this region. 
The blastoderm originates through the migration of yolk cells 
from the interior to the surface of the egg. All of the yolk cells, 
however, do not take part in the formation of the blastoderm, part 
remaining behind to prepare the yolk for assimilation by the embryo. 
After the blastoderm is formed it is one cell thick and covers the 
entire surface of the egg. with the exception of the ovarian yolk. 
The germ band originates in the region of the ovarian yolk, where 
it invaginates and grows downward into the egg. The germ band 
is of the completely submerged type, the uninvaginated blastoderm 
becoming the serosa. 
Upon leaving the surface of the egg the germ band leaves behind 
it a group of cells embedded in a mass of protoplasm. This body 
the junior author has termed the "polar organ." 
