I am in the process of co-authoring an essay on Charles Darwin and the work he did with mollusks, mainly snails (here it is). Thanks to the Darwin Correspondence Project, I've been able to search for relevant information thru the thousands of letters Darwin sent and received during his lifetime.
During the mid-1850s, Darwin experimented with land snails (see this old post). He also tried to raise snails, probably to have more subjects for his experiments. On 14 July 1855, he wrote to his neighbour John Lubbock: "… I got yesterday some more & enough specimens of Helix pomatia for my Snailery."
But apparently he wasn’t always successful in getting the snails to proliferate; in a letter dated 9 October 1856 to an unidentified correspondent, Darwin wrote: "I have been myself keeping Helix Pomatia in confinement all summer, but they have not laid a single egg, so that I have not at all profited by my scheme."
Over the years, Darwin seems to have been quite frustrated by his inability to come up with clear-cut mechanisms to explain the dispersal of land snails, especially to oceanic islands. On 3 October 1856, he wrote to his cousin William Darwin Fox:
No subject gives me so much trouble & doubt & difficulty, as means of dispersal of the same species of terrestrial productions on to oceanic islands.–Land Mollusca drive me mad, & I cannot anyhow get their eggs to experimentise on their power of floating & resistance to injurious action of salt-water.Nevertheless, in On the Origin of Species (1859), he was able to propose two plausible mechanisms by which land snails could be dispersed. I will return to this subject in another post. Now if you’ll excuse me, I have work to do in my Slugery.