6-day old chick embryo viewed under a stereo microscope, LM

A 6-day old chick embryo viewed under a stereo microscope. The developing heart and blood vessels filled with blood are visible (red). At this stage of development, the chorioallantoic membrane forms. This is a vascular membrane found in the eggs of some amniotes such as birds and reptiles, and in mammals this structure forms the placenta. Research in this area is important to screen drugs that could stop vascularisation of a tumour, to cut off a cancer's blood and nutrient supply in order to kill it. This class of drugs are called anti-angiogenic agents. Diameter of the chick embryo is approximately 5 mm.