1. In experiments on eggs of the newt, Triturus alpestris, it was shown that the first cleavage is carried out normally when the internal turgor is completely relieved by the removal of a large fraction of the internal cytoplasm.

2. The furrow can extend and deepen when separated from the deeper parts of the interior of the cell by a strip of cellophane. Thus little or no part can be played by the contraction of astral fibres attached to the cortex. It seems probable that the factors immediately involved in the deepening and extension of the furrow are located in the cortex itself.

3. The bearing of these observations on some current theories of cell division is briefly discussed, and attention is drawn to the probable importance of general cortical movements, which have been detected but not yet analysed.

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