Phagocytes in the axial complex of the sea urchin, Sphaerechinus granularis (Lam.). Fine structure and x-ray microanalysis.

In the axial complex of Sphaerechinus granularis intense phagocytotic activity is encountered. The phagocytes ingest morula cells and other phagocytes; a lysosomal digestion of the phagocytosed cells is suggested. A subdivision into early and late phagocytes is made according to their granular content. Most of the phagocytes possess intranuclear crystalloids that exhibit a filamentous or particulate substructure. Late stages of phagocytes filled with residual bodies and crystalloids leave the axial complex via the lacunar system to be removed through the rectum. X-ray microanalysis reveals a constant presence of iron and sulphur in the crystalloids. The residual bodies contain iron, sulphur, calcium and zinc in varying amounts. This study confirms that one function of the axial complex is excretion.