Zygote, morula, blastocyst, etc. are different stages of early human development, after the inception of life at fertilization.
A blastocyst is a pre-implanted embryo. At this point the embryo is shaped like a hollow ball, with an inner and an outer layer of cells which will continue to differentiate through the individual's lifespan --- however long a human lives.
72 posted on 10/25/2006 12:39:27 PM PDT by Mrs. Don-o
(Mammalia Primatia Hominidae Homo sapiens. Still working on the "sapiens" part.)