On 27 May 1982, an egg-laying site of Onychodactylus japonicus was found on Mt. Hodatsu, Ishikawa Prefecture. Many pairs of stalked rod-shaped egg sacs were attached to stones in the inmost recesses of a small underground cavity where cold springs emerge from under stones to form the headwaters of a mountain stream. Each egg sac contained 6-13 (mean=11.0) eggs, and the number of eggs laid by a single female was 17-25 (mean=22.0).