Quail-chick chimeric hindbrain

Quail-chick embryo chimera at day 5 viewed in parasagital section. The chimera was made by surgically replacing part of the chick hindbrain at day2 with an equivalent piece of quail tissue. The quail graft becomes completely integrated and the quail cells (stained darker brown) can spread into the surrounding chick tissue depending on their position. Proliferating cells (top) do not mix whereas postmitotic cells (bottom) do.