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  2. 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]

  3. Gastrulation - Wikipedia

    en.wikipedia.org/wiki/Gastrulation

    Gastrulation has been studied in many animals, but some models have been used for longer than others. Furthermore, it is easier to study development in animals that develop outside the mother. Model organisms whose gastrulation is understood in the greatest detail include the mollusc, sea urchin, frog, and chicken.

  4. Animal embryonic development - Wikipedia

    en.wikipedia.org/wiki/Animal_embryonic_development

    The blastula develops into a structure called a gastrula through a process called gastrulation. The gastrula then undergoes further development, including the formation of organs ( organogenesis ). The embryo then transforms into the next stage of development, the nature of which varies among different animal species (examples of possible next ...

  5. Embryological origins of the mouth and anus - Wikipedia

    en.wikipedia.org/wiki/Embryological_origins_of...

    An alternative way to develop two openings from the blastopore during gastrulation, called amphistomy, appears to exist in some animals, such as nematodes. [ 3 ] [ 4 ] In humans, the perforation of the mouth and anus happen at four weeks and eight weeks respectively.

  6. Gosner stage - Wikipedia

    en.wikipedia.org/wiki/Gosner_stage

    Gosner stage is a generalized system of describing stages of embryonal and larval development in anurans (frogs and toads). The Gosner system includes 46 numbered stages, from fertilized embryo (stage 1) to the completion of metamorphosis (stage 46). It was introduced by Kenneth Gosner in 1960. [2]

  7. Primitive streak - Wikipedia

    en.wikipedia.org/wiki/Primitive_streak

    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.

  8. Primitive node - Wikipedia

    en.wikipedia.org/wiki/Primitive_node

    Gastrulation then continues along the ventroposterior blastopore lip and posterior streak region, from where cells contribute to ventral and posterior mesoderm. Adding to this, Brachyury and caudal homologues are expressed circumferentially around the blastopore lips in the frog, and along the primitive streak in chick and mouse. This would ...

  9. Polarity in embryogenesis - Wikipedia

    en.wikipedia.org/wiki/Polarity_in_embryogenesis

    In the frog Xenopus laevis, the animal pole is heavily pigmented while the vegetal pole remains unpigmented. [4] A pigment pattern provides the oocyte with features of a radially symmetrical body with a distinct polarity. The animal hemisphere is dark brown, and the vegetal hemisphere is only weakly pigmented.