/ « 
Polar bodies, segmentation of the 
egg and formation of the blastula and 
planula. 
1 Egg soon after it was laid. 
2-3 Formation of polar bodies. 
4-5 Fertilized egg with first seg- 
mentation furrow beginning 
at the upper pole. 
6 The two-celled stage. 
o o 
o 
3 
7 The four-celled stage in forma- 
tion. 
8 The four-celled stage complete. 
9 The eight-celled stage. 
10 Another eight-celled stage. 
11-12 Later stages of segmentation. 
13 A young blastula. 
14 An older blastula, in outline. 
15 A planula. 
16-17 Sectional views of blastulae. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 2. 
