Overlapping cell processes in the embryonic chick retina. Representative labeling of cell proliferation (a), death (b), and differentiation (c), (d) in retinal whole mounts from chick embryos ((a), HH19; (b), HH20; (c), HH23; (d), HH21). Positive cells were scored in 4–6 retinas from different embryos and represented on isodensity maps of the different processes (e)–(g). The insets show positive cells at higher magnification, as employed for scoring. The main morphological features are labeled as follows. ON and *: optic nerve; D: dorsal; V: ventral; T: temporal; and, N: nasal. Scale bars represent 80 μm (a)–(d), 500 μm (e)–(g), and 40 μm (insets).