Each individual of a mating pair tries to shoot a dart into the body wall of the other by forceful eversion of its containing dart sac 1. The dart is coated with mucus from a pair of 4-branched 2 or 5-branched 2.1 mucus glands connected close to the opening of the dart sac. The penis 3 of each is everted, like a sock turned inside out, through the atrium 4and out of the genital pore 5 by hydrostatic pressure of haemolymph (blood). Each inserts its penis through the other’s genital pore and atrium into the other’s vagina 6 which is connected by the bursal duct 7 to the bursa copulatrix and diverticulum where some of the incoming sperm are digested and some stored for later use.

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