Observations on the development of the Xth cranial nerve ganglion in an Urodelan Amphibian (Triturus) have been made. Increase in cellular number, plotted against time, yields a growth curve with two phases of rapid increase, in hatching and in premetamorphosis times (double S-shaped curve). The growth rate curve and the mitotic activity one are similar. The correlation observed between these curves supports the use of mitotic activity as increasing population index also for the nervous system. The ganglionic morphological modifications related to the development of its parts and of surrounding organs have been stated.