The hyaline spheres (HS) in auricularia ofStichopus japonicusconsist of extracellular material in which solitary cells are present. This extracellular material can be stained by dyes for lipids. There are no membranes or other structural elements in HS. The cells within HS are most probably responsible for secreting the extracellular material. HS are not embryonic inductors of the ciliary rings which appear during metamorphosis. They probably store nutrients which permit larvae to complete metamorphosis successfully, but this remains to be established.