Editing Embryology (section)

====Pre-Socratic philosophers====
Many [[Pre-Socratic philosophy|pre-Socratic philosophers]] are recorded as having opinions on different aspects of embryology, although there is some bias in the description of their views in later authors such as [[Aristotle]]. According to [[Empedocles]] (whose views are described by [[Plutarch]] in the 1st century AD), who lived in the 5th century BC, the embryo derives and receives its blood from four vessels in all; two arteries and two veins. He also held sinews as originating from equal mixtures of earth and air. He further said men begin to form within the first month and are finished within fifty days. Asclepiades agreed that men are formed within fifty days, but he believed that women took a full two months to be fully knit. One observation, variously attributed to either [[Anaxagoras of Clazomenae]] or [[Alcmaeon of Croton]], says that the milk produced by mammals is analogous to the white of fowl egg. [[Diogenes of Apollonia]] said that a mass of flesh forms first, only then followed by the development of bone and nerves. Diogenes recognized that the placenta was a nutritional source for the growing fetus. He also said that the development of males took four months, but that the development of females took five months. He did not think the embryo was alive. Alcmaeon also made some contributions, and he is the first person reported to have practiced dissection. One idea, first stated by [[Parmenides]], was that there was a connection between the right side of the body and the male embryo, and between the left side of the body and the female embryo. According to [[Democritus]] and [[Epicurus]], the fetus is nourished at the mouth inside the mother and there are comparable teats that supply this nourishment within the mother's body to the fetus.<ref>Joseph Needham, ''A History of Embryology'', Cambridge 1959, pp. 27-31.</ref> Discussion on various views regarding how long it takes for specific parts of the embryo to form appear in an anonymous document known as the ''Nutriment''.

Ancient Greeks discussed whether only the male had a seed which developed into the embryo within the female womb, or both the male and the female each had a seed that made a contribution to the developing embryo. The difficulty that one-seed theorists confronted was to explain the maternal resemblance of the progeny. One issue that two-seed theorists confronted was why the female seed was needed if the male already had a seed. One common solution to this problem was to assert that the female seed was either inferior or inactive. Another question was the origin of the seed. The encephalomyelogenic theory stated that the seed originated from the brain or and/or bone marrow. Later came pangenesis, which asserted the seed was drawn from the whole body in order to explain the general resemblance in the body of the offspring. Later on hematogenous theory developed which asserted that the seed was drawn from the blood. A third question was how or in what form the progeny existed in the seed prior to developing into an embryo and a fetus. According to preformationists, the body of the progeny already existed in a pre-existing but undeveloped form in the seed. Three variants of preformationism were homoiomerous preformationism, anhomoiomerous preformationism, and homuncular preformationism. According to the first, the homoiomerous parts of the body (e.g. humors, bone) already exist pre-formed in the seed. The second held that it was the anhomoiomerous parts that were pre-formed. Finally, the third view held that the whole was already a unified organic thing. Preformationism was not the only view. According to epigenesists, parts of the embryo successively form after conception takes place.<ref name="wilb">James Wilberding, "Plato's Embryology," Early Science and Medicine 2015.</ref>