Characteristics of the nucleolini observed under the electron microscope.

Observations with the electron microscope permitted us to ascertain that in molluscs and echnioderms oocytes and in malignat tumour cells, the nucleolini, already seen with the phonton microscope, correspond to the "clear fibrillar zones/. These present fibrils 40-60 A thick, spread throughout a very clear matrix. All around these zones there are other closely thickened and interlacing fibrils.