Appearance and disappearance of multiply ciliated follicular cells during development of the dog's thyroid gland.

Multiply ciliated follicular cells have been observed in developing thyroid glands in dogs. These cells are prominent three weeks prior to the expected date of birth but become progressively less common as development proceeds. After birth only rare isolated cilia remain. No evidence of removal of cilia by autophagy or loss into colloid was found. It is concluded that cilia are probably no longer formed by mature cells and that those already present are diluted out by progressive division of mature follicular cells.