Glioblast migration in the optic stalk of the chick embryo.

Light and electron microscopy was used to study the chick embryo optic stalk from Hamburger and Hamilton stages 21 to 29. Observations of glioblast morphology in different developmental stages suggest that these cells undergo radial migration toward peripheral regions of the stalk. Immediately previous to and during migration, morphological changes were noted in the glioblasts, including the appearance of lateral prolongations which contribute to the subdivision of optic fiber fascicles and the radial elongation of their nucleus, which gives the impression of squeezing itself into the peripheral glioblastic prolongation. These phenomena occur in a retino-diencephalic direction, commencing in the distal optic stalk during stage 23 and continuing in subsequent stages. The significance of glioblastic migration is discussed in relation to possible mechanisms through which optic fiber fascicles, initially located on the surface of the stalk, come to lie in deeper areas of the stalk wall.