Basically we can divide the whole cycle into 6 phrase. menstruation, repair phrase, ovulation, receptive phrase, and pre menstrual phrase, all in this order. usually a cycle takes around 28 days, but it can sometimes be longer or shorter depending on different women. for around the first 5 days (again, it's not exact days) it's menstruation, uterus lining is shed out from the vagina. this only occurs if fertilisation and implantation does not take place. then for the next few days, it's the repair phrase, oestrogen helps repair the lining of uterus, to thicken it up, to prepare for fertilisation and implantation, a place for the fetus to develope. next 3 days will be ovulation, where the ovary will release one mature egg (but sometimes 2 or none) into the oviduct, the egg can only survive for a few days so if fertilisation doesn't occur during this phrase, menstruation will occur that cycle. next will be receptive phrase, where the lining keeps on thickening, and the thickness is maintained by progesterone, another female hormone. at last it's the pre menstrual phrase, lining will start to degenerate unless implantation ocured. hope this helps
Gradual changes in the frequency of diseases over long periods are known as SECULAR TIME TRENDS. For example, the rate of mortality in USA due to coronary heart diseases over a period of time. Onset of puberty in girls is also a secular time trend. Secular time trend is also referred as Secular Variation and Secular Drift.
Answer is Middle Paleozoic era. Paleozoic era was in 542 Ma - 245 Ma and it has 6 periods as Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. 360-280 Ma - forming of vascular plants with woody tissues, seeds and veins. 430 - 410 Ma - forming of jawed fishes and first amphibians. 420 Ma - forming of scorpions 360 Ma - forming of crustaceans.
