Early research on anatomy and mating of land slugs and snails: Francesco Redi's (1684) "Osservazioni"

In 1684 the Italian scientist Francesco Redi published one of the first detailed studies on land gastropods. It included the mating and functional anatomy of limacid slugs, functional anatomy of helicid snails and morpho-anatomical comparisons of land and marine slugs and snails. His research was based on a few marine species (an unidentified gastropod, the neogastropod Hexaplex trunculus and aplysiid opisthobranchs), several land snails (including the large helicid Helix lucorum) and some limacid slugs (probably different species of the Limax corsicus group and perhaps Limacus flavus). Redi's investigations are generally accurate and his description of slug mating is much more detailed than the earlier account by Martin Lister. However, his survey also contains minor oversights and mistakes: he did not identify major organs of mollusc anatomy (radula, salivary glands and certain genital structures), his illustration of mating slugs is unrealistic and he overlooked important anatomical differences between marine and land slugs. His most remarkable oversight is hermaphroditism: although he observed slug mating, knew that no differences existed between partners, and was probably aware of earlier literature on the androgynous nature of land snails, he failed to conclude that they are hermaphrodite.