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Map of human skin color distribution for native populations, by R. Biasutti in the von Luschan's chromatic scale for classifying skin color. It was reported that for areas with no data Biasutti simply filled in the map by extrapolation from findings obtained in other areas. [1] Skin colors according to von Luschan's chromatic scale
Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages. At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs.
Human fertilization is the union of an egg and sperm, occurring primarily in the ampulla of the fallopian tube. [1] The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the 19th century. [2]
Drawing of the head of a four-week-old human embryo. From Gray's Anatomy. Embryo drawing is the illustration of embryos in their developmental sequence. In plants and animals, an embryo develops from a zygote, the single cell that results when an egg and sperm fuse during fertilization. In animals, the zygote divides repeatedly to form a ball ...
Insemination is the introduction of sperm (in semen) into a female or hermaphrodite's reproductive system in order to fertilize the ovum through sexual reproduction. [1] [2] The sperm enters into the uterus of a mammal or the oviduct of an oviparous (egg-laying) animal.
In embryology, Carnegie stages are a standardized system of 23 stages used to provide a unified developmental chronology of the vertebrate embryo.. The stages are delineated through the development of structures, not by size or the number of days of development, and so the chronology can vary between species, and to a certain extent between embryos.
(day 20 of fertilization. [1]) Primitive heart tube is forming. Vasculature begins to develop in embryonic disc. (day 20 of fertilization. [1]) Embryo at 4 weeks after fertilization. [3] A 10mm embryo from an ectopic pregnancy, still in the oviduct. This embryo is about five weeks old (or from the seventh week of menstrual age).
This is an accepted version of this page This is the latest accepted revision, reviewed on 11 February 2025. "Skin pigmentation" redirects here. For animal skin pigmentation, see Biological pigment. Extended Coloured family from South Africa showing some spectrum of human skin coloration Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among ...