Primary cilia of the corneal endothelium.

A primary cilium is a normal component of every rabbit corneal endothelial cell, rather than being a rare or sporadic organelle, as previously believed. In common with other cilia of this type it possesses an axonemal organization of 9 +0 which converts distally to 8 + 1; it occurs only one per cell; and the basal body is accompanied by a proximal centriole. Additional structures associated with the basal body are nine transitional fibers, four striated satellite arms, and several rootlets. Ladderlike structures extend between the two centrioles to form the wall of a barrel. Reexamination of primary cilia from other tissues indicates that the ultrastructure of endothelial cilia may be characteristic of primary cilia in general.