Search results
Results from the WOW.Com Content Network
In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external fertilization. The fertilized egg cell is known as the zygote. [2] [5]
Due to the fact that placental mammals and marsupials nourish their developing embryos via the placenta, the ovum in these species does not contain significant amounts of yolk, and the yolk sac in the embryo is relatively small in size, in comparison with both the size of the embryo itself and the size of yolk sac in embryos of comparable developmental age from lower chordates.
Embryology is the subdivision of developmental biology that studies embryos and their development. The main article for this category is Embryology . Contents
Gastrulation in frogs commences in the marginal zone— the region encircling the blastula's equator where the animal and vegetal hemispheres meet—differing from sea urchins where it begins in the most vegetal part. In contrast to the vegetal blastomeres, the endodermal cells in the marginal zone of frogs are smaller and contain less yolk. [2]
Observing embryos of different species, he described how animals born in eggs (oviparously) and by live birth (viviparously) developed differently. He discovered there were two main ways the egg cell divided: holoblastically , where the whole egg divided and became the creature; and meroblastically , where only part of the egg became the creature.
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst, is reorganized into a two-layered or three-layered embryo known as the gastrula. [1]
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.
Also gastrocoel. The central internal cavity of the gastrula in most animal embryos, fated to develop into the lumen of the digestive tube ; the primitive gut. The archenteron initially has only one open end, known as the blastopore. B birth blastocoel Also blastocoele, blastocele, cleavage cavity, and segmentation cavity. The fluid-filled or yolk -filled cavity that forms in the developing ...