42 
from five minutes to an liour after impregnation the egg 
becomes quite regularly spherical, as shown in Figure 1, and 
is now covered by a distinct limiting membrane^ which ad- 
heres closely to the surface of the uniformly granular yolk. 
The changes of segmentation take place so very rapidly 
that the close observation of the living egg demanded all my 
attention, and I was not able to make any observations upon 
stained specimens, regarding the fate of the germinative vesi- 
cle, or the orgin of the polar globules or formation of the first 
segmentation nucleus; and the living egg is sufficiently opaque 
to prevent observations upon this point. 
After the egg has assumed the spherical form shown in Fig- 
ure 1, it remains without change for some time, usually nearly 
an hour, and then enters upon a period of activity, during 
which changes follow each other with great rapidity. 
The first thirteen figures were drawn from the same egg. 
As the day was very cold, the changes were slow, and the 
first period of activity did not set in until two hours and 
seven minutes after impregnation, but the series of changes 
shown in Figures 2-13 occupied only seventeen minutes, and 
this was so much longer than usual that I w T as able to com- 
mence my series of drawings by sketching them. 
As shown in Figure 2, the egg commences its activity by 
elongating and becoming oval, with one end narrower than 
the other. The narrow end is to become the nutritive pole, and 
the broad end the formative pole of the segmenting egg. In 
all the figures of segmenting eggs the formative pole is above,, 
and the nutritive below, and the latter corresponds, in a gene- 
ral way, to the dorsal surface of the embryo. 
Contractions now begin to make their appearance at the 
formative end, throwing the limiting membrane into waves or 
wrinkles, which travel rapidly towards the formative pole, 
near which they disappear. 
The wrinkles are shown in Figure 2. It is, of course, 
impossible to show their movement in a drawing, but the 
progression over the surface of the yolk, from the starting- 
point at the smalf end to the place where they disappear near 
the round end, is w'ell marked, and is a constant characteristic, 
