sexuality. Dual sexuality or hermaphroditism as found in the pulmonates is also known in some species of Acmaea Limpets, Janthina, Odostomia, Stilifer, Valvata and the Paper Moon Snail, Velutina. The sexuality of this type, however, is more of the consecutive type, in which the gonads at first produce sperm and later in the season only eggs.
Sex reversal is especially characteristic of the Slipper Shell family. The best known examples belong to the Cup-and-saucer Shells, Calyptraea and Crucibulum, and the true Slipper Shells, Crepidula. Individuals function as
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Figure 7. Sex reversal in the Slipper Shells, Crepidula, a to e, animal with shell removed to show the development of the verge in the male phase; f and g, atrophy of the verge and the change to the female phase; h, a group of attached Crepidula fornicata, showing the smaller males (♂) at the top and the females (♀) below; i, Crucibulum spinosum with the small male attached to the female. (After W. R. Coc 1943.)
the male sex when young and as females when fully grown. The change-over may be gradual with the individual being ambisexual for a short period, or the male phase may suddenly disappear with the loss of its associated organs, and the female organs may then quickly develop. The males are much smaller than the females. In most species, each young male tends to creep about until it finds an individual of the same species in the female phase, whereupon it attaches itself to the dorsal side of the female’s shell in a position adjacent to the female copulatory organs (fig. 7i). In other species the
