Embryonic cleavage is the division of cells without cell growth. Once an ovum is fertilized by a sperm cell, it is called a zygote. The zygote undergoes multiple rapid cell cycles (rounds of mitosis) without significant growth, producing a dense cluster of cells that is the same size as the original zygote. This process is called cleavage.

Embryogenesis is the process by which an embryo forms, and begins with fertilization of an ovum by a sperm cell. Once an ovum is fertilized, it is referred to as a zygote. The zygote undergoes rapid mitotic divisions without any significant cell growth, a process called cleavage. After four cell divisions occur, a ball of sixteen cells is produced, which is called the morula. After the seventh cleavage, a ball of 128 cells called the blastula is produced. The blastula allows the addition of the G1 and G2 phases into the cell cycle, permitting the cells to grow in size before dividing. The blastula develops an inner cell mass and trophoblast, and becomes implanted in the uterine lining. A gastrula is formed when cells migrate to the interior of the blastula and form three germ layers: the endoderm, mesoderm, and ectoderm. A neurula forms after differentiation of the ectoderm forms the primitive central nervous structures.

The correct order of the early development is: cleavage, implantation, gastrulation, neurulation.

Cleavage occurs when zygote undergoes many mitotic divisions without cellular growth, becoming a morula and then a blastula. Only after becoming a blastula will the cells begin to grow in size.

Implantation occurs during the blastula stage when the embryo becomes implanted in the uterine lining.

Gastrulation occurs when the three germ layers (endoderm, mesoderm and ectoderm) arise from the blastula. At this stage, the embryo is considered a gastrula.

Neurulation occurs when the germ layers develop a primitive nervous system, transitioning the embryo from a gastrula to a neurula.

Cleavage occurs immediately after fertilization. It is a rapid process that increases cell number without increase cell size. Essentially, cells divide without any G1 or G2 phase of the cell cycle. The result is several very small cells that take up the same volume as the original singular zygote.

Cleavage generates the morula and, later, the blastula during development. At the blastula stage, the cells develop the G1 and G2 phases of the cell cycle and begin more comprehensive development. At this stage, the embryo begins to differentiate the inner cell mass and trophoblast regions.

Implantation of the embryo occurs during the blastula stage.

The zygote is initially formed by the process of fertilization in the fallopian tube. As the zygote travels within the tube, it begins to undergo cleavage, developing into a morula and eventually a blastula. By this point, it has entered the uterus and can become implanted in the uterine lining. The blastula then begins to differentiate, developing the three germ layers, and becoming a gastrula via the process of gastrulation.

The blastula, or blastocyst, is made up of blastomere cells and a fluid-filled cavity called the blastocoel. 

There are two regions of the blastocyst: the inner cell mass and the trophoblast. The inner cell mass gives rise to the primitive endoderm and the epiblast, which later gives rise to the three germ layers during gastrulation. The trophoblast is the layer of cells forming the outer ring of the blastocyst. It secretes factors to make the blastocoel and is kept separate from the inner cell mass. All fetal structures eventually develop from the inner cell mass, while the trophoblast helps maintain the fetal environment and placenta.

The blastula consists of a hollow sphere of cells (blastomeres) surrounding an inner fluid cavity called the blastocoel. There are two regions of the blastula: the inner cell mass (embryoblast) and the trophoblast. The inner cell mass gives rise to the primitive endoderm and epiblast, serving as the site of the developing embryo. The trophoblast cells form the outer ring of the blastocyst and combine with the maternal endometrium to form the placenta.

The inner cell mass, or embryoblast, gives rise to the cells that become the fetus.

A blastula is a sphere of cells (blastomeres) surrounding a fluid blastocoele. The blastula stage of embryogenesis begins with the appearance of the blastocoel. The blastocoel is a fluid filled cavity that contains amino acids, proteins, growth factors, and other components neccessary for cellular differentiation. The blastocoel allows blastomeres to move during gastrulation.

A morula is a solid ball of cells within the zona pellucida and is a precursor to the blastula.