Which of the following is the correct order of stages in human embryonic development?
Morula, Blastocyst, Embryo, Foetus
After fertilisation, the zygote divides repeatedly to form a spherical mass of cells called morula. This gradually develops into the blastocyst, which is a hollow sphere of cells with a surrounding single cellular layer, and an inner cell mass. This gets implanted into the uterine wall, and by 3 weeks, it can be called an embryo. Further development of organs continues, and by 8 weeks, the embryo develops into the foetus. The foetus undergoes gradual changes, and typically, by the end of 40 weeks, the infant is born.