Slugs are hermaphroditic. In a successful mating, both individuals receive sperm from each other, so the earlier sexual stage is male, and the later one is female, as the presence of a spermatophore initiates the production of eggs.

The hermaphroditic gland has two functions. First it gives rise to sperm,and then to ova. They both travel through the hermaphroditic duct and the sperm oviduct.

From this point in my explanation I must say that I don't know how some of these processes happen... The sperm first travels the oviduct, maturing under the influence of the prostate gland, which for most of the way encases the duct. At some stage it passes through the narrow vas deferens which joins the intromittent organ which in some slugs is called the penis, and in others the epiphallus. When a mating slug recieves a spermatophore from its partner, it is stored in the bursa, where part of its cuticle (case) is dissolved and the sperm released to fertilize the eggs.

When the ova begin their journey, they have something done to them by the albumen gland at the end of the hermaphroditic duct. The albumen gland enlarges in the female stage, a very opaque, white organ with the look and consistency of tallow. It is not very flexible and breaks easily in dissection.

At the top of the oviduct (which is still called the "sperm oviduct") is a muscular chamber called the "capsular duct" where each egg is squeezed into shape, and just as it is ejected into the genital pore, its shell is put on, or applied somehow.