SEGMENTA HON. 



63 



Fig. 29. — Modes of segmentation. 

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



blastosphere, e.g. Hydra. 

 s*. Ovum, with considerable yolk (jr.) at lower pole, segments totally 



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



3. Ovum, with much yolk (y.) at lower pole, segments partially and 



discoidally, forming blastoderm (bl.\ e.g. bird. 



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



e.g. crayfish. 



