Thyroid follicles in a cat thyroid gland, light micrograph. In this species, the follicles have a small average size, so much so that, at times, they do not seem to exist. The visible colloid in the follicles shows a slight retraction, being separated from the epithelium. Reabsorption vacuoles (clear rounded 'punched out' areas generally located at the edge of the colloid) stand out, formerly interpreted as evidence of colloid reabsorption by thyrocytes, they are in fact artifacts..