The motion picture is concerned with the following topics: I. the composition of the nucleolus which is shown to consist of two parts: a) the unstructured nucleolar substance, and b) filamentous structures which prove to be Feulgen-positive and are regarded as representing parts of the nucleolar chromosomes; 2. the form of the nucleolus which is variable, depending on the condition of both components; 3. the discharge of nucleolar material which may occur when the nucleolus is attached to the nuclear membrane; 4. the relations between the behaviour of the nucleolus and the mitotic events.