The zygote passes through several developmental stages till implantation. Describe each stage briefly with suitable diagrams.

The following figure shows various stages of zygote development till implantation: 
(a) The zygote divides into a two-cell stage called cleavage. This development takes place when the zygote is still in the isthmus. 
(b) The cleavage undergoes further rounds of mitosis to form 2, 4. 8, and finally 16-celled stage. These daughter cells are called a blastomere. 
(c) The 16-celled stage is called the morula. 
(d) The morula changes into blastocyst; with more rounds of meiosis. At this stage, the blastomeres are arranged in an outer layer of cells: called trophoblast and an inner mass of cells. 
(e) Implantation to the uterine wall happens at the blastocyst stage.