Camelids, New World/anatomy & histology; Placenta/ultrastructure; Placentation; Pregnancy/physiology; Acid Phosphatase/metabolism; Alkaline Phosphatase/metabolism; Animals; Camelids, New World/metabolism; Capillaries/metabolism; Capillaries/ultrastructure; Cell Size/physiology; Chorion/blood supply; Chorion/metabolism; Chorion/ultrastructure; Endometrium/metabolism; Endometrium/ultrastructure; Epithelial Cells/metabolism; Epithelial Cells/ultrastructure; Female; Immunohistochemistry; Metrial Gland/metabolism; Metrial Gland/ultrastructure; Microscopy, Electron; Microscopy, Electron, Scanning; Microvilli/metabolism; Microvilli/ultrastructure; Placenta/metabolism; Placental Lactogen/metabolism; Trophoblasts/metabolism; Trophoblasts/ultrastructure