Eggs! I found them late last night under the leaves on the bottom of the tank. This is good news, because it shows that the 2 slugs (Megapallifera mutabilis) I have been keeping since December are doing well enough to reproduce. Furthermore, the eggs will not only provide more slugs for future experiments, but they may also help me learn a bit about their development. In fact, I may start examining them as early as tonight.
The masses below the eggs are fecal strings or slug poop. They are dark colored because of the green algae the slugs eat.