The construction of the insect compound eye: The involvement of cell displacement and cell surface properties in the positioning of cells

The highly patterned arrangement of cells in the Ephestia compound eye arises in an orderly spatiotemporal sequence from a small population of cells organized into ommatidial precursors ("differentiation center"). The presumptive retina cells in the posterior region of this zone differentiate in an anterior to posterior order before differentiation proceeds in an anterior direction from the zone. The bidirectional growth of the compound eye from the differentiation center cannot be ascribed solely to an inductively transmitted "wave of differentiation"; the spreading of an epithelial sheet of cells bordering the center is, at least in part, involved in this process. This latter statement is based on the observation that when genetically marked tissues are transferred from the eye regions of donor pupae to the corresponding sites of host pupae, the grafts are displaced along the antero-posterior head axis, either in an anterior direction or a posterior direction depending upon their original positions relative to the differentiation center. The tissues derived from pupal grafts transposed or reoriented along this same axis often experience striking configurational changes and axial displacements. Findings of this nature support the hypothesis that cells of the prospective adult eye possess position-specific differences in cell adhesiveness.