64 REPRODUCTION AND LIFE HISTORY OF ANIMALS. 



Fig. 12. —Modes of segmentation. 



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

 blastosphere, c.i^.. Hydra. 



2. Ovum with considerable yolk (j') ^t lower pole se.i^nieius wholly 

 hut unequally, C-g.^ frog ; O'--^-) larger yolk, laden cells. 



3. Ovum with much yolk segments partially and discordally, 

 forming blastoderm (/'/.), e.g., bird. 



4. Ovum with central yolk 0') segments partially and peripherally, 

 e.g.., crayfish. 



