the mating behaviour of this species has been particularly well studied, partly to provide taxonomic characters. mating starts when one individual closely follows the flattened tail of the other (precourtship). typically after some minutes the leader turns back and protrudes its sarcobelum (a tapering finger-like part of the penis), as does its partner shortly afterwards. the partners often form a circle head to tail. early courtship involves violent biting of the partner, lashing the sarcobelum against the partner, and bursts of tail wagging. this is gradually replaced by more gentle-looking stroking of the sarcobelum across the partner. during courtship, sperm accumulates in the penial caecum. after about 90 minutes the partners orient themselves face-to-face, nibble the base of the partner's raised sarcobelum, and suddenly their penises simultaneously evert. the finger-like penial caecum curves round the back of the partner's sarcobelum, transferring sperm onto it. the penes remain everted for a variable period (typically some minutes) before the penial lobe and then the penial gland also evert. the latter transfers a secretion onto the partner. this is directly followed by retraction of the penis (each partner thereby taking up the transferred sperm) and then separation.