Fig. 7.

Comparison of the number of side-branches per millimeter of preterminal axon in monkey (magno,stippled bar; parvo, black bar) and in cat (dotted bar). The number of axons analyzed is indicated on top of each bar; standard error bars are shown. For each length of axon, the total number of side-branches was counted and divided by the total axon length of each fiber. Total axon length refers to the entire extent of a parent axon within the DLGN that could be visualized in a 200 μm section. In cat, side-branches are prevalent at early fetal ages, dropping dramatically by E57. In monkey, side-branches on both parvo and magno axons are few and relatively constant during the time that eye-specific laminae are being formed. The fetal cat data at E48, E54, E57, and E65 are derived from Sretavan and Shatz (1986), their Figures 6 and 7, whereas the E50 data were obtained in our laboratory from DiI-labeled fibers.