“…Derrick (1937) reports that the high mitotic rate in the sides of the chick medullary plate as compared with the floor may aid neurulation in that form. In this animal it has also been found that after the neural tube has closed, incidence of mitosis is higher in the evaginating optic vesicles than it is in other regions of the brain (Frank, 1925). Hutchinson (1940), on the other hand, finds that the elongation of the neural tube which occurs soon after its closure in Amblystoma is not due to cell proliferation.…”