Slide 9 Thyroid
The C-cells secrete calcitonin which helps lower calcium levels. Recall that this hormone antagonizes the effect of PTH from the parathyroids. These C-cells are actually named for being "clear" (as in lighter staining). Notice that they are in the interstitium and do not normally touch the follicles.

Bar = 50 Microns

Notice again the simple cuboidal epithelium lining the follicles.
Expanded View