Qualitative and quantitative freeze-fracture studies on olfactory and respiratory epithelial surfaces of frog, ox, rat, and dog. IV. Ciliogenesis and ciliary necklaces (including high-voltage observations).

A comparison of the necklaces of sensory olfactory, and non-sensory nasal respiratory cilia of four vertebrate species (frog, ox, rat and dog) shows that the olfactory cilia have 7 +/- 1 (mean +/- standard deviation) strands in the three mammalian species and 6 +/- 1 strands in the frog; for the respiratory cilia these values are 5 +/- 1 and 4 +/- 1. This function- and species-dependency of ciliary necklace strand numbers is supported by a review of the literature. Necklaces show no other structural differences. Necklace strand densities range from 25--33 strand/micrometers. In both sensory and non-sensory cilia ciliogenesis is preceded by the formation of necklace strands. Sometimes cilia do not develop properly, as demonstrated by the presence of necklace-like structures in the membranes of olfactory dendritic endings and respiratory axonemal aggregates.