Implantation in the Plains Viscacha, Lagostomus Maximus

Summary. Accurately dated pregnancies were obtained in order to determine the time and mode of implantation in the plains viscacha, Lagostomus maximus. Implantation was completely interstitial and occurred antimesometrially on Day 18 post coitum. From each animal, very large numbers of single-celled and fragmenting eggs and relatively few blastocysts were flushed from the uterus up to the time of implantation. They were found at the ovarian end of the uterine horns, indicating that the blastocysts do not become spaced until just before implantation. Up to five blastocysts implanted progressively in each horn from the cervical to the ovarian end. No morphological or histological differences could be detected along the length of the uterus. The significance of these findings is discussed in relation to the fact that only those fetuses nearest the cervix in each uterine horn survive whilst the others are resorbed early in pregnancy.