66 A'EPJWDUCTION AND LIFE HISTORY OF ANIMALS. 



central cavity — the segmentation cavity — and a hollow ball 

 of cells — a blastosphere or blastula — results. 



Fk;. 13. — Life liistury of a coral, Motuwi-iiia Dai'ivinii. 

 (From II.KCKEL. ) 



A, 1!, Ovum C, Division into t«o. I), Four cell st.-ii;e E 

 Blastula. P , Free swimmuig bla.stula with cilia. G, Section of 

 blastula. H, Beguining of invagination. 1, Section of completed 

 gastrnia showing ectoderm, endoderni, and archcnteron, K Free 

 swimming ciliated gastrnia, ' 



