The zygote first develops into a morula(solid ball of cells) and then a blastocyst (hollow ball of cells and fluid), before it is implanted in the inner lining of the uterus. The inner lining is called the endometrium, and is rich in blood vessels and glands. These structures provide nutrients to the blastocyst as well as secrete proteins which stimulate the implantation process, and growth and development of the blastocyst.