Abstract: On the evidence available from the present study in the Petrous ganglion, the dark cells are considered as active ones and the light cells are considered as resting, inactive, dying or degenerating cells. Cell death is most prominent and common among the small and medium sized ones. Probably, it is during these developmental stages, peripheral and central processes (of axons) begin to grow from the cell body and get established in their projection fields. The tiny cells are always dark. The very-small cells are also usually dark during embryonic development till E18. The light cells have appeared among this cell group just on the day of hatching.
During the late stages of development (around E15 - E18). the phagocytosis is too fast that the inactive, dying or dead cells (I. e., so-called light cells) are removed immediately as soon as they are formed so as not to leave such a light-cell stage for clear observation. The light-cell stage becomes clearly observable only when the phagocytic process is slow, and this becomes prominent at a time when some of the important connections are being actively established.
The fluctuation in the number of cells during embryonic development may be considered as a normal process for the purpose of re-arrangement and better organization to perform an orderly function most efficiently. The period of accelerated degeneration or loss of cells is the period of active establishment of proper connections of ganglion cells. The reduction or loss in the number of neurons in the adult ganglion might indicate a functional reduction probably as a result of aging process.