Cytological changes induced by low temperature in the thyroid glands of larvae of the salamander Hynobius retardatus

摘要: Abstract In order to study the environmental conditions and endocrine mechanism which induce neotenous characteristics, fine structure of thyroid glands larvae salamander Hynobius retardatus were examined. The exposed a low temperature (4°) compared with those higher (20°). At 4°, follicular lumen was large its contents electron density; epithelial cells flat or cuboidal. contrast, 20° showed small dense tall cylindrical cells, may indicate level activity. No apical vesicles found in 4° larvae, although they present larvae. On other hand, chromatin nuclei scattered, while it condensed. addition, granules occupied 2.4% cytoplasm as much 7.3% structural features observed cold resembled reported for made inactive by lack thyrotropin.