[Differention of the neural tube. Experimental study in chick and quail embryos]

In order to study the possible influence of adjacent structures upon differentiation and proliferation of the chick spinal cord, a piece of neural tube of chick embryos incubated for 2 days (stages 12-14 of HAMBURGER and HAMILTON) was extirpated and replaced by an equal graft from a donor embryo of the same age. The grafts were rotated 90 or 180 degrees around their longitudinal axis. The examination of the serial histological sections and the analysis of the distribution of mitotic density in the rotated spinal cord of embryos fixed 2-8 days after the operation led to the following results: the differences in morphogenesis and histogenesis between dorsal and ventral sectors of the spinal cord are already determined in 2-day-old chick embryos. The reversal of the neural tube at this time has no effect either upon the typical differentiation or the characteristic distribution of the mitotic cells in the spinal cord.