The Editor and the Publisher regret that Figures 1 to 4 in this article were printed with a reduction incompatible with the required resolution in electromicrographs. They apologize for any inconvenience resulting from this error. The figures are being reproduced at larger sizes and at resolutions more compatible with the originals in the following pages. −→ Fig. 1 -Ultrathin sections of opossum's optic nerve fibers, 24 (A and B) and 48 hours (C and D) after crush. A. Normal fibers (n) are seen

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... among some altered fibers, which exhibit watery degeneration (star) and myelin sheath breakdown (thick arrow). Note demyelinated fibers (thin arrows) with an apparently intact axoplasmic cytoskeleton. Asterisk, astrocytic processes. Bar = 1.7µm. B. Normal looking optic nerve fiber (n) is seen above an optic fiber showing dark degeneration (star). Bar = 0.4µm. C. Longitudinal section of optic nerve fibers showing areas of focal degeneration of the axoplasmic cytoskeleton (star). Asterisk, astrocytic processes; m, mitochondrial profile. Bar = 0.6µm. D. Observe optic nerve fibers with an apparently normal appearance (n). Among them, there is a fiber with dense axoplasm and some altered organelles, typical of dark degeneration (d). Asterisks, astrocytic processes. Bar = 0.6µm.