In a little wood in Oegstgeest (near Leiden, Netherlands) patches of slime, sometimes with slime tracks leading up to them, were found on a number of beeches (fig. 1, 2) and oaks in August 1959. It was practically proved that these slime marks were traces of the copula of Limax maximus, when on a visit at about 11 p.m. specimens of that species ascending these trees were seen by torch light. On September 19, 1959, such patches were found in the southeastern corner of the little wood on three beeches (from 1.35 to 1.70 m above the soil) and on nine oaks (from 0.85 to 1.50 m above the soil).