Abstract
Summary
Locomotor reactions have been observed in Fundulus heteroclitus embryos abnormal in number and arrangement of Mauthner's neurones. Five out of 11 embryos lacking Mauthner's axones on one or both sides of the cord were abnormally passive or immobile; the remaining six exhibited vigorous swimming movements. Out of 7 embryos in which the 2 Mauthner's fibers coursed posteriorly both on the same side of the cord, 2 were abnormally passive and 5 exhibited vigorous movements. Axones from supernumerary Mauthner's cells were present in the cord in 22 embryos; one of these embryos was abnormally passive, but the others exhibited no variations of behavior attributable to the altered number of Mauthner's fibers. The apparently negative results of the experiments in which supernumerary axones were added, and the fact that asymmetry in the arrangement of fibers was not reflected in asymmetry of reaction, demonstrate a high degree of regulability of function in the developing brain of Fundulus.
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