Hayashi and Carthew (Nature 431 [2004], 647) have shown that the packing of cone cells in the Drosophila retina resembles soap bubble packing, and that changing cadherin expression can change this packing and cell shape. We here ask which surface mechanics are involved in the establishment of cell topology and geometry. We model, using a minimal set of parameters based upon experimental observations, the topology and geometry of wildtype cone cells, as well as mutants with different amounts of cells or changed expression of cadherin molecules. We show that cell packing is not the result of overall surface area minimization, which is the case in soap bubble packing, but of adhesion-driven cell extension limited by a contractile cell cortex.