 In cell biology , the nucleus ( pl. nuclei ; from Latin nucleus or nuculeus , meaning kernel ) is a membrane @-@ enclosed organelle found in eukaryotic cells . Eukaryotes usually have a single nucleus , but a few cell types , such as mammalian red blood cells , have no nuclei , and a few others have many . 
 In cell biology , the nucleus ( pl. nuclei ; from Latin nucleus or nuculeus , meaning kernel ) <a href='drop_aux' title='1'><mark>is</mark></a>a membrane @-@ enclosed organelle found in eukaryotic cells . Eukaryotes usually <a href='got' title='2'><mark>have</mark></a> a single nucleus , but a few cell types , such as mammalian red blood cells , <a href='got' title='3'><mark>have</mark></a> no nuclei , and a few others <a href='got' title='4'><mark>have</mark></a> many . 
In cell biology , da nucleus ( pl. nuclei ; from Latin nucleus or nuculeus , meaning kernel ) a membrane @-@ enclosed organelle found in eukaryotic cells . Eukaryotes usually got a single nucleus , but a few cell types , such as mammalian red blood cells , got no nuclei , and a few others got many .