The origin, distribution and disappearance of surface cilia during embryonic development of Rana pipiens as revealed by scanning electron microscopy

Abstract

AbstractCilia begin to grow from the free surface of some ectodermal cells during the neural plate stage (stage 13). Ciliary growth is not closely synchronized between cells in the same embryo, but the number of ciliated cells increases greatly during neural fold development and further growth in length of pre‐existing cilia occurs. Ciliated cells are numerous and widely distributed over the surface of early tailbud stages. However, cilia do not develop on cells in the neural plate and inner sides of the neural fold, and only an occasional ciliated cell is observed on the surface of the paired suckers. The number of ciliated epidermal cells per embryo increases during tail growth (stages 18–22). Ciliated epidermal cells persist after hatching (stage 20), but regression of cilia can be detected in stage 24 larvae. By late stage 25, most of the cilia have disappeared and the morphological variations observed indicate that the process involves resorption of cilia. Non‐ciliated (secretory) ectodermal cells from the neurula onward to stage 25 synthesize granules which are released to provide a mucous‐like coat for the embryo and larva. The surface structure of both ciliated and non‐ciliated ectodermal cells is described in sections studied with the transmission electron microscope and compared to the surface architecture of both cell types observed with the scanning electron microscope.