The polarization of cells during development is discussed with relationship to synchronized cell divisions and lineage restrictions. A tessellation model is proposed to explain the generation of the precise hexagonal array of ommatidia in the eye. This model allows the assembly of highly organized structures from localized cellular interactions. There is no requirement for a precise genetic description of the adult organism. Instead a sequential set of reiterated cellular interactions generates increasingly complex structures. The polarity patterns observed in adult cuticular bristles and hairs reflect accurate control of the shape of terminally differentiating cells rather than fine-grained positional information.