This remarkable instrument, which is known as a “Love-dart,” or _Spiculum amoris_, assumes a different form in each species in which it occurs. In some the shaft is ridged like a bayonet, as in the case of the Garden Snail, in others the form assumed is that of an awl. These darts are formed within a special receptacle, or “dart-sac,” but so far no explanation as to the origin of these remarkable structures has even been hinted at. They do not seem to have been derived by the modification of some pre-existing organ serving a different function, as wings, for example, are derived from walking limbs, or as lungs are derived from air-sacs. Their origin is as mysterious as their use: for they are not found in all Snails, though they occur in one or two Slugs—which are degenerate Snails. But no other Molluscs save the Snails and one or two of their immediate allies are so armed. The hermaphrodite conditions of these animals, as with other Mollusca in like case, present some knotty points for consideration, and especially in regard to the problem of sex-attraction. Where each individual is as much male as female, which is the dominating factor in desire, the maleness or the femaleness? Though each individual contains both ova and sperm cells, probably these ripen at different times, to avoid danger of self-fertilization. In this case the sex impulses are on the same footing as in the case of animals wherein the sexes are not thus combined. That is to say, the individual which is for the moment only potentially male mates with another for the moment only potentially female. But this being so, how does each discover the condition of the other?