English: Monotremes are oviparous which means that they produce eggs with a lot of (2) yolk inside of the (3) yolk sac so that most of the embryonic development can take place outside of the female reproductive tract. Within the uterus of the female momotreme a (1) double layer shell is secreted around the (5) embryo. This is later surrounded by a third layer. The (4) allantois is used for gas exchange. The (5) embryo is inside of an (7) amniotic membrane which is filled with (6) amniotic fluid. Source: http://www.ansci.wisc.edu/jjp1/ansci_repro/misc/project_websites_08/thur/monotremes/embrdevel.html