Associated with the follicles (*) are clusters of lightly stained parafollicular or C cells (C). These cells contain and secrete calcitonin, somatostatin and, in some animal species, serotonin.

These C cells are located inside the basement membrane delimiting a follicle but are separated from the colloid by the epithelial follicular cells.

Stain: H–­­E
Magnification: ×900