64 REPRODUCTION AND LIFE HISTORY OF ANIMALS. 



FIG. 12. Modes of segmentation. 



1. Ovum with little yolk segments totally and equally into a 

 blastosphere, e.g., Hydra. 



2. Ovum with considerable yolk (y) at lower pole segments wholly 

 but unequally, e.g., frog ; (y.s.) larger yolk, laden cells. 



3. Ovum with much yolk segments partially and discordally, 

 forming blastoderm (bl.), e.g., bird. 



4. Ovum with central yolk (y) segments partially and peripherally, 

 e.g., crayfish. 



