Early embryology and implantation in the California leaf-nosed bat, Macrotus californicus.

Female reproductive tracts from 84 bats were examined by light and/or electron microscopy to electron microscopy to observe early embryology and implantation in Macrotus. The earliest pregnancy was observed in October and by the end of October all bats were pregnant. Implantation had begun in most specimens from late October. In late November females were carrying implanted blastocysts in which differentiation of endoderm was noted. Reichert's membrane was first observed in November. In early December the trophoblast had begun to differentiate into cytotrophoblast and syncytiotrophoblast and by the end of January this differentiation was most evident. Reichert's membrane persisted until late January. Endoderm in the January sample completely surrounded the yolk sac cavity. By late February the embryos were at the embryonic disc stage had differenitated mesoderm. The uterine-fetal relationship was complex and an early placenta was recognized. In late March the embryos spanned a range of development from neural plate to limb-bud stages. Parturition occurred in June. This lengthy gestation period is characterized by an embryonic diapause of approximately four and one-half months. The roles of food supply and/or temperature in controlling this growth rate and the evolutionary implications of this development are discussed.