LARVAL FUSION AND DEVELOPMENT OF CONJOINED TERATOIDS IN BIOMPHALARIA-GLABRATA

Snails of a genetically isolated laboratory stock of Biomphalaria glab rata, if mated to snails of certain other stocks, produce polyzygotic egg capsules. When two or more embryos occupy a single capsule, some e mbryos spontaneously fuse during the trochophore larval stage into ter atoids of usually two, but up to seven, conjoined snails. We have obse rved more than 950 of these fused teratoids, with some dizygotic conjo ined twins surviving to adulthood. Allophenic cell-to-cell adhesions l ead to unusual patterns of development, apparently determined by the a reas of the embryos that are fused.