what differences are there in the reproductive development of monotremes marsupials and eutherian mammals
Figure 3. Representative monotreme (echidna; a,c) and marsupial (tammar wallaby; b,d) reproductive systems. In females (a,b) the ureters pass medially preventing fusion to form a single uterus as occurs in most eutherian mammals. In male monotremes (c) the testes are held within the abdominal cavity, whilst in most male marsupials (d) the testes descend into a scrotum (not shown) anterior to the penis.
Birth and early development in Eutheria. Eutherians, like their closest relatives the marsupials, give birth to live young. In eutherians, however, the young are nurtured within the body of the mother by the placenta, which allows nutrients to pass from the blood of the mother almost directly into the blood of the young. The placenta also allows oxygen to reach the developing young, thereby making more energy available than in marsupials.