Garden snails, Cornu aspersum, in process of mating. The picture shows two snails from below; the crinkled foot of each covered with mucus. They are coupled at the smooth white region just to the right of picture centre. C. aspersum is hermaphrodite; each snail contains sperm and egg cells. Mating is initiated by firing a small sharp calcareous dart (visible here, below centre, to left) to pierce the surface of a potential partner. The target withdraws into its shell, pauses, then emerges and fires its own dart at the initiator. The genital atrium of each snail is then everted, and they join together, as here. Copulation follows; each snail inserts its penis through the conjoined atria, and exchange of spermatophores follows. The snails stay conjoined for up to an hour; both as mothers-to-be. Darting success is not always required. The dart in this picture failed to pierce its target