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Abstract
Thyroid follicle cells of a facultively neotenic salamander ( Ambystoma tigrinum ), a perpetual perennibranchiate ( Necturus maculosus ), and a consistently partially metamorphosing derotreme ( Amphiuma means ), were compared at light and electron microscopic levels. In all three urodeles, a feltwork of cytoplasmic filaments apparently becomes contractile and is responsible for relatively rapid changes in cellular configuration. It apperars that microtubules form as an intermediate step in the synthesis of new filaments. The paucity of parafollicular (light) cells may be partly responsible for the lack of ossification in adult perennibranchiates. While recent evidence suggests that little T 4 is produced and none is released into the blood stream by Necturus thyroid ( 42 ), morphologically, the follicle cells appear to be relatively active. Detection of small amounts of T 4 in the thyroid of this genus may merely represent a disappearing function for this gland. Therefore, it might prove useful to look for other functions for the follicle cell of Necturus without the preconceived notion that it only synthesizes iodinated tyrosines.
Published Version
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