This investigation is an attempt to provide a chronological account of the ontogeny and significance of changing pattern of the neuronal elements in the vagal (nodose) and vestibular ganglia of the chick. Two types of morphologically different neuron-types (dark and light ones) are observed. The dark cells are considered to be active ones, while the light-cells are effete cells, i.e., inactive, dying, dead or degenerating ones which have failed to establish or lost their functional connections. Since the small and medium sized cells are the youngest stages in which the light cells make their first appearance, it is assumed that the establishment of functional connections might begin around the very-small and small cell stage during embryonic development. The appearance of light cells among the very-small ones just on the day of hatching possibly signifies their attempt to eliminate the growing cells since they are no longer needed to replace larger categories of cells which have already well-developed neuronal connections by the day of hatching. In the vagal ganglion is the occurrence of large number of light-cells on E6 from this behavior, it is assumed that the vagus nerve establishes the earliest functional connections (around E6 or even earlier) in view of its vital functions involved in maintaining the life of animal during development because of its connections with vital organs concerned with alimentary, respiratory and cardiac functions. In the vestibular ganglion, the appearance of a few light cells on E6 might indicate the beginning of an early establishment of functional connections in contrast to most other ganglia studied. It is possible that proper maintenance of vestibular function in order to keep the different organs (such as heart, lung, liver, intestine, brain etc) in their most suitable position during early stages of development in relation to the gravitational force, is possibly an important factor for proper development and growth of every organ and system of the body, and to the life of the individual at large.