Ciliary development was studied in the cells of the neural canal of chick embryos incubated from 60 hours to 7 days.
It was found that centrioles move after the last mitosis to the cell periphery where one of them enters into contact (terminal contact) with the cell membrane; the other centriole remains close by, its axis aligned along the axis of the former.
The cell membrane was seen afterwards bulging at the contact point, and the content of the ciliary bud thus formed is only constituted at the beginning of a varied number of vesicles of about 140 Å diameter.
The ciliary bud becomes elongated shortly after filaments start becoming organized in the bud matrix.
Roughly coinciding with the initiation of filament organization the centrioles move inward and the cilium becomes deeply invaginated in the cell. At the end of ciliary growth the centriole moves again toward the surface and the cilium emerges in the neural canal lumen.