Embryonic Stages 



Modern Organisms 



Ovum 



Amoeba 



Chiamydomonas 



Cleavage Stages 



Pandorina 



Blastula 



Volvox 



Ectoderm 

 Endoderm 

 Blastopore- 



Archenteron 



Mouth 



Gastrula 



FIG. 4.15. Parallelism between early stages of embryonic development and mod- 

 ern organisms representing levels of organization which may possibly have char- 

 acterized stages in the evolution of the metazoa. 



