Prenatal Development after Diapause in the Marsupial Macropus rufogriseus

Abstract

Prenatal development of Macropus rufogriseus was described in eight stages ranging from a quiescent blastocyst to a near-term foetus. Embryos and corpora lutea were induced to resume development after diapause by the removal of suckling pouch young (RPY). The diameter of unilaminar blastocysts ranged from approximately 260 µm at 0 days after RPY to 290 µm after 6 days. At 9 days after RPY (330 µm diameter) the zona pellucida and mucoid coat were apparently absent and endoderm had proliferated (early bilaminar). At 15 days, mesoderm had formed in the trilaminar blastocyst (4.8 mm diameter). By 18 days after RPY the shell membrane had ruptured and was 3.0 µm in thickness (7.0 pm at 0 days after RPY). At this time the pre-foetal embryo had acquired forelimb ridges, mesonephric kidneys, optic stalks and 25 paired somites; persistent features included an amniopore, posterior neuropore and an intact stomodeal membrane; the lung buds and allantois were rudimentary; cervical, lumbosacral and cranial flexures were present. By 20 days after RPY, digital anlagen were noted in the forelimb paddles of the pre-foetal embryo (32 paired somites); the gonadal ridges; glomeruli and optic cups had formed. At 25 days after RPY, the near-term foetus had forelimbs with claws on the separate digits, hindlimb paddles, pontine flexure and cardiac valves; the metanephric kidneys, pigmented and nervous retinas and villous intestine were present. A single birth was recorded at 26 days after RPY (delayed gestation length).