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Amphibians are notable as remnants of the first vertebrates capable of surviving in both aquatic and terrestrial environments. [1] The embryonic development of tailless amphibians is presented below using the African clawed frog ( Xenopus laevis ) and the northern leopard frog (Lithobates pipiens ) as examples.
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]
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 ...
Sperm entry can occur anywhere in the animal hemisphere. [2] The point of sperm entry defines the dorso-ventral axis - cells opposite the region of sperm entry will eventually form the dorsal portion of the body. [1] [3] In the frog Xenopus laevis, the animal pole is heavily pigmented while the vegetal pole remains unpigmented. [4]
The archenteron is labeled as the digestive tube. The filopodia—thin fibers formed by the mesenchyme cells, found in late gastrulation—contract to drag the tip of the archenteron across the blastocoel. The endoderm of the archenteron will fuse with the ectoderm of the blastocoel wall. At this point gastrulation is complete, and the embryo ...
Cell fate studies have revealed that also the overall temporal sequence in which groups of endomesodermal cells internalize along the frog blastopore and amniote primitive streak are surprisingly similar: the first cells that involute around the amphibian blastopore lip in the organizer region, and that immigrate through Hensen's node ...
[1] [2] Embryonic development begins with a sperm fertilizing an egg cell to become a zygote, which undergoes many cleavages to develop into a ball of cells called a morula. Only when the blastocoel is formed does the early embryo become a blastula. The blastula precedes the formation of the gastrula in which the germ layers of the embryo form. [3]
[2] [3] It is the first fluid-filled cavity or lumen formed as the embryo enlarges, [4] and is the essential precursor for the differentiated gastrula. [5] [page needed] In the Xenopus a very small cavity has been described in the two-cell stage of development. [6]