Cell division in the developing cat retina occurs in two zones.

Cytogenesis in the kitten retina has been investigated with [3H]thymidine autoradiography and a stain for mitotic figures. The nuclei of cells in S-phase are located adjacent to the inner margin of the cytoblast layer, near the inner plexiform layer. The nuclei then migrate toward the outer limiting membrane (OLM) to divide. Evidence is presented that in a small population of mitotic cells, the nucleus does not migrate to the OLM, but divides in the inner part of the cytoblast layer or, after the outer plexiform layer has formed, in the inner nuclear layer. Cell division in this inner zone begins and ends later than at the OLM. Cells dividing there are fewer in number than those at the OLM, their mitotic spindles are oriented randomly rather than parallel to the retinal surface and their nuclei move little between S- and M-phases of the mitotic cycle. The zones of cytogenesis at the OLM and in the inner cytoblast layer resemble, respectively, the ventricular and subventricular zones of other areas of the developing central nervous system.