356 WHEELER. (Vo. ITT. 
endowed with amoeboid tendencies, for when the ectodermic 
wall is about to be completed in the median dorsal line these 
cells are seen to have accumulated at the place of closure. The 
amniotic cells, which have become applied to the surface of the 
yolk by the bending back of the two folds resulting from rup- 
ture, have closed in the yolk while the serosa is separating from 
it. The advancing body walls of the embryo, however, soon 
make the amniotic covering unnecessary, and it contracts in the 
median dorsal line to form what may be called an ammnzotic dorsal 
organ, to distinguish it from the sevosa/ dorsal organ of latta. 
Figure 90 is a part of a section through the median dorsal por- 
tion of an embryo in the stage represented in Fig. 74. At do 
the protoplasm of the amnion has thickened, and the nuclei are 
seen passing in between the yolk bodies. At are a number of 
nuclei undergoing degeneration. These resemble the degener- 
ating entoderm nuclei to which I have called attention in a much 
younger stage. The amnion cells, which have become applied 
to the yolk when the membrane ruptures, enter the yolk after 
the formation of the dorsal organ by the very narrow slit left 
in the closing ectoderm in the median dorsal line. This is seen 
somewhat indistinctly in Fig. 85. Nuclei are observed at 6 
passing in between the two cardioblasts (cd, cb), which are about 
to meet and form the heart. The splanchnic mesoderm (s/w), 
with the underlying entoderm, still leaves a wide gap through 
which the migration into the yolk takes place. The granular 
matter surrounding the nuclei is probably the remains of the 
cytoplasm of the amnion cells. In the figure a number of entire 
Figures 14-16.— Three diagrammatic median cross-sections through the egg of 
Doryphora, before and during revolution. ch. chorion; v. vitelline membrane, ap- 
plied to the inner face of the chorion; @. amnion; s. serosa; e#. embryo; do. dor- 
sal organ (amniotic); y. yolk. 
