A physical mechanism of micelle formation in homopolymer systems is elucidated. The mechanism is applicable in particular to melts of stereoisomeric polymers, for example, polystyrene. It is hinged on aggregation and crystallization of occasional atypical stereoregular fragments of mostly irregular (atactic) polymer chains. Phase diagrams involving the regimes of lamellar, tapelike, and disklike semicrystalline micelles are obtained and discussed. The possible relevance of the theory to the puzzling anomalous cluster phenomena observed in homopolymer melts (low-frequency solidlike rheological behavior; low-q excess light scattering-Fischer cluster modes) is discussed as well.