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The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed using Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"—is a historical hypothesis that the development of the embryo of an animal, from fertilization to gestation or hatching (), goes through stages resembling or representing successive adult stages in the evolution of the ...
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 ...
Leonardo studied human embryology with the help of anatomist Marcantonio della Torre and saw the fetus within a cadaver. [2] The first study, measuring 30.5×22 cm, shows the fetus in a breech position inside a dissected uterus.
Specifically, Haeckel's critics accused him of manipulating the embryo drawings to make the early stages of different species look more similar. They claimed that the drawings of four-week dog and human embryos had been copied without attribution from other sources, and changed by expanding dog's head and reducing the human head, moving the eye ...
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The primitive streak is a structure that forms in the early embryo in amniotes. [1] In amphibians, the equivalent structure is the blastopore. [2] During early embryonic development, the embryonic disc becomes oval shaped, and then pear-shaped with the broad end towards the anterior, and the narrower region projected to the posterior.
Soranus of Ephesus, Gynaecology, in a Latin version of late antiquity: positions of the embryo in the uterus. The illustrations in this manuscript of c. 900 are probably based on drawings by Soranus. Brussels, Bibliothèque Royale, Codex 3714, fol. 28r.
The observation of the conservation of animal morphology during the embryonic phylotypic period, where there is maximal similarity between the species within each animal phylum, has led to the proposition that embryogenesis diverges more extensively in the early and late stages than the middle stage, and is known as the hourglass model. [5]