 A second model proposes that proto @-@ eukaryotic cells evolved from bacteria without an <unk> stage . This model is based on the existence of modern <unk> bacteria that possess a nuclear structure with primitive pores and other <unk> membrane structures . A similar proposal states that a <unk> @-@ like cell , the <unk> , evolved first and <unk> archaea and bacteria to generate the nucleus and the eukaryotic cell . 
