Advanced oviductal development, transport to the preferred implantation site, and attachment of the blastocyst in captive-bred, short-tailed fruit bats, Carollia perspicillata

The final stages of embryonic development in the oviduct, transport of the embryo to the uterus, and the initial stages of implantation have been exam ined in captive-bred Carollia perspicillata at the light and electron micro scopic levels. Development progressed to the expanded, zona pellucida-free, blastocyst stage in the oviduct. The abundance of microvilli on the exteri or of the trophoblast Varied with the degree of blastocyst expansion and ce ll shape, and may function ill part as a membrane reservoir. Cells of the b lastocyst also typically contained many lipid droplets and prominent areas of cytoplasm occupied by finely granular material (probably glycogen) inste ad of organelles. In most females, closure of the uterine lumen occurred pr ior to, or around the time of, transport of the blastocyst to the usual imp lantation site and appeared to play a role in preventing: transport of the blastocyst too far distally in the uterus. This was associated with increas ed endometrial edema, particularly in the fundic region of the simplex uter us, and the extravasation of many erythrocytes into the endometrial stroma. Both of these changes began while the blastocyst was still being held in t he oviduct and became pronounced during implantation. Engulfment of these e rythrocytes by processes of the endometrial stromal cells and their phagocy tosis by macrophages was also observed. Implantation was usually initiated within narrow tubular segments, lined by endometrium, that were located bet ween the end of each oviduct and the main cavity of the uterus, or from imm ediately adjacent areas of the main cavity. During the early stages of impl antation, thr: blastocyst was clasped by the endometrium at the implantatio n site, and this was associated with extensive interdigitation of the micro villi of the trophoblast and adjacent uterine epithelial cells. Initial adh esion of the trophoblast, which was still cellular rather than syncytial, o ccurred over the apical intercellular junctions of the uterine epithelial c ells.