Fig. 7.

Branches extend from active regions of the axon after varying delays after the primary growth cone has resumed forward advance. A, Series of images showing an example of a branch (arrow) extending at a right angle simultaneously with forward advance of the primary growth cone. This gives the appearance of growth cone bifurcation. B, Series of images showing an example of a branch (arrow) extending after a delay of 47 hr after the primary growth cone has resumed forward advance. By 23 hr the primary growth cone has emerged from the growth cone that is still pausing at 22 hr. By 69 hr the branch (arrow) is extending interstitially from the active region on the axon. C, Frequency histogram showing numbers of branches that extended after varying delays after the primary growth cone had resumed forward advance. D, Frequency histogram showing numbers of branches that extended from the axon at varying distances behind the primary growth cone.