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Abstract The fine structure of the cerebellar cortex in rats was examined between the first and forty‐fifth post‐natal day. The formation and growth of axon and dendrites are reported here. As inferred from these observations, the process starts under the cell membrane as a local accumulation of vesicles without any visible content, about 1,100 Å in size. This is followed by an outward bulging of the membrane which then becomes filled with vesicles and is known as the primary growth cone. In axons the synaptic and growth cone vesicles coexist until the third week or longer. In dendrites secondary growth cones exist at the tip of the branching dendrites and spines. Variations in the shape of the growth cone vesicles related to the age of the animal are described, and the importance of attempting to isolate the growth cones and the vesicles is emphasized.
Cerro et al. (Mon,) studied this question.