sarcobela slightly contract and point upwards. The anterior parts of the slugs swell and roll slightly over to the left. There may be biting and touching around the genital pore areas with mouths and tentacles, as well as mutual head swinging. The slugs press their genital pores against each other and pull their mantles backwards. It is also during courtship that the ejaculate is prepared; sperm flows from storage into the penis and, in some species, is assembled into packages such as spermatophores. Love darts In the final stages of courtship, some species of land slugs and land snails shoot calcareous or chitinous love darts into each other's bodies. Only a subset of those species that mate face to face in a simultaneous reciprocal manner bear darts. Both slugs in a mating shoot at each other unless a dart is unavailable, for example because it is being regenerated after a recent mating. Most research into love darts has been performed on the common garden snail, in which it has been shown that dart shooting increases paternal reproductive success through the delivery of mucus which promotes sperm storage rather than digestion in the dart recipient. Control of sperm movement is achieved through reconfiguration of the recipient's copulatory canal prior to sperm receipt. It is only after dart shooting that actual mating takes place. Mating Mating refers to the phase of sperm transfer and lasts from the beginning of penis eversion to the moment the genitalia lose contact with the other slug. Duration varies considerably between slug species but sudden eversions and very brief transfers are most common. Sperm transfer can be simultaneously reciprocal or unilateral, and external (as in Deroceras) or internal (as in Ariolimax). Received sperm is either digested or used for the fertilisation of eggs. Simultaneous reciprocal mating versus unilateral mating In simultaneous reciprocal mating, both slugs act as males and females at the same time. This manner of mating requires that the pair of genitalia be exactly opposed prior to copulation, a task made difficult in slugs as they have no sense of hearing and very limited vision. Hence, they rely heavily on chemoception and contact sensation. There is usually an exchange of sperm, but one-way sperm transfer can occur in certain cases. In unilateral mating, each individual has a defined sexual role: one acts as a male and donates sperm while the other acts as a female