PLATE I. 
Figure 1. — Eggs two hours and seven minutes after fertili- 
zation. It is now perfectly spherical, with an external mem- 
brane, and the germinative vesicle is not visible. 
Figure 2. — The same egg two minutes later. It is now 
elongated ; one end is wider than the other, and a transparent 
area at the broad end marks the point where the polar glob- 
ules are about to appear. At the opposite end the external 
membrane is wrinkled by waves which run from the nutritive 
towards the formative pole in rapid succession for about fif- 
teen seconds. 
Figure 3. — The same egg two minutes later. 
Figure 4. — The same egg two minutes later. The yolk has 
become pear-shaped. The polar globule has appeared at the 
formative pole, in the middle of the broad end of the pear, 
and the nutritive end of the egg is now less granular than 
the formative end. 
Figure 5. — The same egg two minutes later. Three equi- 
distant furrows have made their appearance, separating it into 
a single mass at the nutritive pole, and two at the formative 
pole. At this stage the three masses are about equal in size. 
Figure 6. — The same egg two minutes later. The first mi- 
cromere, o, is now perfectly separated, and smaller than the 
second, b y and each is smaller than the macromere, a. 
Figure 7. — The same egg one minute later. Both micro- 
meres are separated and are spherical, as is also the macromere. 
This stage ends the first period of activity. 
Figure 8. — The same egg forty-five seconds later. The two 
micromeres have begun to fuse with each other, and the second 
mieromere, b, is also partially fused with the macromere, a. 
Figure 9. — The same egg one minute later. The first mi- 
cromere, c 9 has also begun to unite with the macromere. 
