Talk about the nucleoles.

According to rate of protein synthesis one or more dense structures called nucleoli are visible by LM and EM. Disappear during early cell division and reappear during late telophase. Not bound by any membranes and mainly composed of rDNA and proteins, in addition to DNA necessary for its formation. They arise from the NOR which are rDNA or rRNA encoding regions. They are sites for active transcription of rDNA into rRNA (45s) and making *28s 18s 5,8s) and assembly of rRNA with ribosomal proteins