Reconstitutive ability of axial tissue in early rat embryos after operations and culture in vitro.

Longitudinal incisions have been made in the axis of 10-day-old rat embryos (post-neurula stage with 5-10 pairs of somites) at mid-trunk levels, dividing the axis into right and left halves. The embryos have then been cultured in vitro by New's method and their ability to reconstitute tissues in each half has been studied. After 20 h culture at 37 degrees C, there was no longer any external sign of the division of the axis. Histological studies showed that in nearly all cases, however, the neural tube was duplicated in the operated region. The two neural tubes lay in close contact in the midline, and ventral to them the gut was single. Apart from four cases in which the gut roof was slightly broadened and forked, all other tissues were normal. The reconstitutive ability of the neural and gut tissue has been compared with that of amphibian and avian embryos, as observed in 'twinning' experiments by other workers. The apparent delay in axial rotation in the operated rat embryos, as compared with controls, is attributed to the inability of the two separated halves of the somite series to co-ordinate their contractions. Further details of the rotation process in operated embryos will be the subject of a future study.