Classification system originated in the 18th century, from the works of a Swedish botanist Carolus Linnaeus. He classified living beings based on similarities between them. Organisms which could interbreed were put in one species.
During the menstrual phase of the menstrual cycle, the zona pellucida develops around each egg.
The menstrual cycle is count from the first day of one period to the first day of the next period. The menstrual cycle differs in all women. This cycle has four main phases namely the follicular phase, ovulation phase, luteal phase and the menstrual phase.
The follicular phase starts on day one. The follicle stimulating hormone or FSH and estrogen rise. This is followed by the ovulation phase in which the egg is released. In the luteal phase corpus luteum produces progesterone and estrogen. In the menstrual phase of the menstrual cycle, the zona pellucida develops around each egg.
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