Which of the following intracellular structure does NOT have cell membrane?

The nucleolus is a generally spherical, highly basophilic structure present in the nuclei of cells active in protein synthesis. The intense basophilia of nucleoli is due not to heterochromatin, but to the presence of densely concentrated rRNA which is transcribed, processed, and complexed into ribosomal subunits in that nuclear region. Nucleoli are always associated with nuclei of cells that are intensely synthesizing proteins. Nucleolus does not have a limiting membrane and the nucleolus consists of distinct subregions with different staining characteristics. Ref: Mescher A.L. (2010). Chapter 3. The Cell Nucleus. In A.L. Mescher (Ed), Junqueira's Basic Histology: Text & Atlas, 12e.