74 SYDNEY J. HIOKSON. 



Fig. 13. — A section of a young embryo, which shows yolk segmentation. 



Fig. li. — A section through an older embryo, the yolk being omitted, 

 showing the first stages in the formation of the ectoderm (ect.). ee. Ecto- 

 derm, en. Endoderm of the gonophore. 



Fig. 15. — A section through a still older embryo, showing a later stage in 

 the formation of the ectoderm and its connection with the central endoderm 

 Plasmodium. 



Fig. 16. — A solid planula of Distichopora, just before it escapes from the 

 gonophores. 



Fig. 17. — A small portion of the endodermic Plasmodium more highly 

 magnified. Some of the smaller yolk granules are omitted. 



Fig. 18. — a, b, c, d, e. Six stages in the division of the nuclei of the 

 ectoderm. 



