• Describe the concepts of the 3-layered, embryonic germ disc and cephalo-caudal and lateral folding

the creation of the 3 layered disc is called gastrulation,

from the stage of the 2 layerd bilaminar disc there are two layers in this stage one of which lines the yok sac called the hypoblast cells and one of which is the epiblast cells ontop, eventually the epiblast cells leak through into the space between the two cell layers just described, when this occurs the epiblast cells are now known as mesoderm cells and this has created the layer of mesoderm cells thereby creating the trilaminar disc

the mesoderm is known to become the genito-urinary system

• Describe how the germ layers, yolk sac and allantois contribute to the formation of the genito-urinary tracts

the allantois is the original passage out of the waste produced in the fetus out of it through where the adult umbilical belly button is. when the bladder and ureters are formed and the rectal and urinaey tracts are differentiated/partitioned. the allantois becomes urachus which is a tendonous reminant of the allantois. this is known as the median umbillical fold.