1. Basophil cytoplasmic substance of the cells concerned in neural induction in the chick was investigated by methyl green-pyronin staining and the action of ribonuclease. Comparison of a number of stages indicated that changes in both distribution and concentration occur.

  2. Most of the basophil substance was in the dorsal zone of the cytoplasm in presumptive neural and presumptive mesodermal epiblast. In the subsequent differentiation of neural epithelium and chorda-mesoderm its concentration throughout the cytoplasm of both cell-groups increased considerably.

  3. The highest concentrations observed developed in a sharply localized zone at the ventral poles of the cells of the neural groove in its early stages and in some somite cells.

  4. The time relationships of concentration changes in adjacent cells did not indicate whether concentration of the substance at the base of the neural epithelium depends on transfer from other cells.

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