Regrowing nerve fibers are seen in the regenerating newt (Triturus viridescens) optic nerve as early as the fourth postoperative day (4 p.o.d.). The first fibers are found growing through gutters, troughs or tunnels formed by glial cell processes which may serve as pathways to direct the fibers. By 6 p.o.d. regenerating nerve fibers exist in scattered “clusters” growing about the path established by the first fibers. By 10 p.o.d. the clustered appearance is replaced by a more uniform distribution throughout the regenerating nerve.

Beginning with 6 p.o.d. there are increasing signs of spontaneous loss of some regenerating axons. By 21 p.o.d. the loss reaches a peak. The loss appears to be accompanied by continued ingrowth of new fibers. Even as late as 117 p.o.d. the optic nerve population is still not stable for there are signs both of continued nerve growth as well as spontaneous axon loss. Glial myelination of regenerated fibers sets in about 117 p.o.d. and proceeds from the initial lesion centrally toward the optic tectum. There appears to be a direct relation between axon diameter and the initiation of myelination.