Source of the tentacular hormone in terrestrial pulmonates

Summary Collar cells around the optic tentacles of pulmonate gastropods were shown to have a stimulating effect on spermatogenesis in vivo and in vitro. No hormonal action was found in the tentacles other than in collar cells. Therefore, collar cells are considered to be the source of the so-called tentacular hormone in stylommatophoran pulmonates. We propose to name the collar cell group optic gland.