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This constitutes the so-called capsule of the space. Each lacuna is generally occupied by a single cell, but during the division of the cells, it may contain two, four, or eight cells. Lacunae are found between narrow sheets of calcified matrix that are known as lamellae (/ l ə ˈ m ɛ l i / lə-MEL-ee).
Human embryology is the study of this development during the first eight weeks after fertilization. The normal period of gestation (pregnancy) is about nine months or 36 weeks. The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus .
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 ...
Biological patterns such as animal markings, the segmentation of animals, and phyllotaxis are formed in different ways. [2]In developmental biology, pattern formation describes the mechanism by which initially equivalent cells in a developing tissue in an embryo assume complex forms and functions. [3]
When Haeckel was a student in the 1850s he showed great interest in embryology, attending the rather unpopular lectures twice and in his notes sketched the visual aids: textbooks had few illustrations, and large format plates were used to show students how to see the tiny forms under a reflecting microscope, with the translucent tissues seen ...
Aerenchyma in stem cross section of a typical wetland plant. Aerenchyma or aeriferous parenchyma [1] or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. [2]
The embryo map is a sequence of 3-D images, or slices of 3-D images, of the developing embryo which, if viewed rapidly in temporal order, forms a time-lapse view of the growing embryo. The embryogenic tree is a diagram which shows the temporal development of each of the cell lines in the embryo.
From his observations of these stages in different vertebrates, he realised that Johann Friedrich Meckel's recapitulation theory must be wrong. For example, he noticed that the yolk sac is found in birds, but not in frogs. According to the recapitulation theory, such structures should invariably be present in frogs because they were assumed to ...