THE JOURNAL OF EXPERIMENTAL ZOOLOGY 238:129-139 (1986) Stimulation of Genital Eversion in the Land Snail Helix aspersa by Extracts of the Glands of the Dart Apparatus

The dart apparatus, used during courtship in some groups of hermaphroditic land snails, has long been assumed to have a “stimulatory” effect on the mating partner, though how stimulation occurs and exactly what function it serves has never been determined. In this study, extracts of the mucous glands of the dart apparatus of the land snail Helix aspersa were injected into conspecifics and into a related snail, Cepaea nemoralis, in order to test the hypothesis that the dart is used to achieve inflow of bioactive mucous gland secretions into the darted snail. Helix aspersa injected with the extract responded by everting their terminal genitals; eversion normally takes place during courtship and mating. Boiling the extract increased the bioactivity. Pronase-treated extract lost bioactivity, and gel filtration of the boiled extract indicated that the active substance has a molecular weight of about 5,000. The active substance may be a polypeptide. Cepaea nemoralis also everted their genitals when injected with the boiled Helix extract. The active substance appears to be a contact sex pheromone, the second such pheromone in a pulmonate land snail for which experimental evidence has been obtained. Accessory organs in the terminal genitalia of the hermaphroditic land snail order Stylommatophora (reviewed by Tompa, ’84) include calcareous or chitinous spears or darts that are thrust into the mating partner during courtship. About 11 of the 65 families of pulmonate land snails possess a dart apparatus, comprising a dart held in a dart sac and associated glands (Tompa, ’80). In addition, at least two families of opisthobranchs possess darts (see Pruvot-Fol, ’60; Boss, ’82). In the Euthyneura (pulmonate snails and sea slugs), a dart apparatus may have evolved independently in at least seven different major lineages. Because of its use in courtship, it has long been assumed that the dart is a “stimulatory” device in courtship and mating (see Dorello, ’25; Bornchen, ’67; Tompa, ’84 for reviews), though this has never been proven. The hypothesis that the dart is used to stimulate the courting partner mechanically and thereby induce mating is very old (e.g. see Moquin-Tandon, 1855; Cooke, 1895; Meisenheimer, ’07). Goddard (‘62) has suggested from experiments on isolated penis sheaths of Helix aspersa that damage of tissue by the dart might cause increased tonus of the penial muscles. The hypothesis that the mucous glands associated with the dart apparatus (= dart glands or multifid glands) might secrete stimulatory substances during courtship has been advanced by Dorello (‘25) and Bornchen (’67). Dorello (’25) found that H. aspersa injected with secretions of the mucous glands contorted their bodies and showed, after dissection, increased stiffening of the penis. Bornchen (‘67) found that extract of the mucous glands of H. pomatia increased the frequency and amplitude of the heart beat. However, Goddard (’62) found no effect of mucous gland extract on contraction of a penial sheath preparation of H. aspersa. Other hypotheses on the function of the mucous glands include: lubrication for the dart and genitals, formation of the egg shell, and formation of the dart (Meisenheimer, ’12; Moquin-Tandon, 1855; also see Bornchen, ’67 and Tompa, ’84 for reviews). It is now known that the mucous glands do not form either egg shell or the dart. In recent observations on mating behavior in helicids, Lind (‘761, Jeppesen (’761, and