3) parafollicular cell single between follicular cell in small groups in interstitial tissue structure LM ovoid, polygonal /arger /pale-stained: eosinophilic /argyrophilic granules3) parafollicular cell ---single between follicular cell ---in small groups in interstitial tissue ---structure: LM: /ovoid, polygonal /larger /pale-stained: eosinophilic /argyrophilic granules