Spermatogenesis takes approximately 64 days in adult humans. Males begin producing sperm at puberty, and continue until death.

Oogenisis halts in the female embryo while the oocytes are trapped in meiosis II. At the beginning of the menstrual cycle a number of oocytes in primordial follicles are stimulated by pituitary gonadotropins to continue maturation.

Parthenogenesis is the activation and development of an egg without sperm. Parthenogensis, therefore, is not sexual reproduction, but can still result in a fully developed offspring.

Isogamy is a condition of indistinguishable male and female gametes, but they retain the ability to join in sexual reproduction. Hermaphroditism and pseudohermaphroditism are rare conditions in which a single organism produces both sperm and eggs and is able to self-fertilize in sexual reproduction.

The menstrual cycle has four phases: 

1) Menstrual phase (days 1-5): the uterus sheds its lining, which exits the body through the vagina in the form of menstrual fluid.

2) Follicular phase (days 1-13): the pituitary gland releases a hormone that stimulates the egg cells to grow. One egg cell matures in a sac-like follicle for 13 days; while it is maturing, the follicle releases a hormone that causes the uterus to develop its lining.

3) Ovulatory phase (day 14): the events listed in the question occur.

4) Luteal phase (days 15-28): the egg released during ovulation stays in the fallopian tube for 24 hours, disintegrating if not fertilized during that time. During this phase, the hormone that causes the uterus to retain its lining is used up, causing another menstrual phase to begin.

Hormone balance is extremely important in both developing the male and female fetus. Hormone levels can regulate and determine the relative level of sex characteristics that we see in individuals. Both sexes produces testosterone and estrogen, but utilize the hormones in different ways. Testosterone is produced at higher levels in males and is used to develop male secondary sex characteristics. Estrogen is produced at higher levels in females and is used to develop female secondary sex characteristics.

Progesterone is a secondary sex hormone that is also produced in both sexes. Females use progesterone to regulate the menstrual cycle, and levels of the hormone vary in women.

After fertilization occurs, the zygote undergoes a series of cellular divisions in a process called cleavage. This is followed by the formation of the blastula, a hollow sphere of cells. Gastrulation occurs next, where the embryo is divided into three germ layers: the endoderm, mesoderm, and ectoderm (from inside to outside). Hence, gastrulation is the stage in which this process first occurs. Neurulation and organogenesis occur after gastrulation.

Once a committed cell begins to develop specialized functions, it is known as differentiation. Before a cell differentiates, it makes a commitment to a certain cell type, first by specification, which is reversible, and then by determination, which is irreversible. Once a cell is committed to a cell type, it undergoes differentiation to develop specific cell characteristics.

Induction is a process in which cells induce adjacent cells to commit to a certain cell type. 

The gastrula is formed during the second week following fertilization. At this stage, a process called gastrulation takes place. During gastrulation, the three primary germ layers are formed: the ectoderm, the mesoderm, and the endoderm.

Prior to gastrulation, the embryo is a blastocyst, and prior to that it is a morula. The morula forms soon after fertilization and is classified by cleavage divisions, increasing the number of cells without increasing the size of the embryo. The blastocyst is characterized by the formation of the inner cell mass and trophoblast; implantation occurs during this stage. After implantation, gastrulation occurs. After the gastrula stage, the embryo begins the process of neurulation (development of the primitive streak and notochord) and becomes a neurula.

The correct order is listed below.

1. Fertilization: the joining of an egg and sperm

2. Cleavage: early cell division in an embryo before a specific structure is formed

3. Blastula Formation: the cells of the embyro form a hollow structure filled with fluid

4. Gastrulation: the cells in the embryo migrate to form the three germ layers; the hole with fluid formed during the blastula stage is now filled with cells

Gastrulation is the phase in embryogenesis in which the single-layered blastula is reorganized into a trilaminar structure called the gastrula. These three germ layers are called the endoderm, mesoderm, and ectoderm and give rise to individual organs during organogenesis.

The blastula is implanted into the uterine lining and the morula undergoes rapid cell divisions (cleavage) after fertilization of the zygote.