Embryologically, the bladder is derived from the urogenital sinus, and it is initially continuous with the allantois.
12.
The first to evolve was probably the allantois, a sack that develops from the gut / yolk-sack.
13.
It is formed by the fusion of the mesodermal layers of two developmental structures : the allantois and the chorion.
14.
Later came the amnion surrounding the fetus proper, and the chorion, encompassing the amnion, allantois, and yolk-sack.
15.
The allantois, along with the amnion and chorion ( other embryonic membranes ), identify humans, and other mammals, as amniotes.
16.
Additional factors that are important in HSC migration during this period are Integrins, umbilical arteries and the allantois, in which HSCs and endothelial cells are colocalized.
17.
Further development of the design, like extraembryonic membranes ( amnion, chorion, and allantois ) and a calcified shell, were not essential and probably evolved later.
18.
:The umbilical cord develops from the embryonic allantois; it will have the baby's DNA . As you've correctly deduced, the placenta is indeed entirely Mom's.
19.
Although Haeckel is proven right about the allantois, the utilization of Krause s embryo as justification turns out to be problematic, for the embryo is that of a bird rather than a human.
20.
This bend becomes dilated into a pouch, which constitutes the "'endodermal cloaca "'; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward.
