blastocoel

biological cavity

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June 22, 2026

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The blastocoel is a fluid-filled cavity found within a blastula, which is a hollow sphere of cells formed during early embryonic development. This cavity plays a crucial role as the embryo transitions from the blastula stage to the gastrula stage, a process known as gastrulation. In mammals, this early stage is called a blastocyst, and its cavity is also referred to as the blastocoel. The blastocoel is essential for the subsequent rearrangement and specialization of cells that will form the three primary germ layers: ectoderm, mesoderm, and endoderm.1234

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4 Britannica Sources

blastula
blastocoel
animal development - Amphioxus, echinoderms, and amphibians
prenatal development - Cleavage and blastulation

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- blastula
  …enclosing a fluid-filled cavity, the blastocoel. After the blastula develops, it undergoes transition to the gastrula (q.v.), a process called gastrulation. In organisms such as mammals, the earlier morula (q.v.), a berrylike cluster of cells, develops into a somewhat different form of blastula, the blastocyst (q.v.).
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  …enclosing a fluid-filled cavity, the blastocoel. After the blastula develops, it undergoes transition to the gastrula (q.v.), a process called gastrulation. In organisms such as mammals, the earlier morula (q.v.), a berrylike cluster of cells, develops into a somewhat different form of blastula, the blastocyst (q.v.).
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- gastrula
  …has contracted or eliminated the blastocoel, which was the cavity of the blastula, but a new cavity is formed in the hollow of the cup. This primitive gut cavity is the endoderm and forms the rudiment of the animal’s future gut and many of its associated digestive organs and glands.…
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  …has contracted or eliminated the blastocoel, which was the cavity of the blastula, but a new cavity is formed in the hollow of the cup. This primitive gut cavity is the endoderm and forms the rudiment of the animal’s future gut and many of its associated digestive organs and glands.…
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animal development
Cleavage
…and the fluid-filled cavity the blastocoel. In discoidal cleavage the cells, which do not surround the whole embryo, lie only on the animal pole; nevertheless, a blastocoel may be formed by a crevice appearing between the blastomeres and the mass of yolk. The blastomeres then may be arranged as a…
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…and the fluid-filled cavity the blastocoel. In discoidal cleavage the cells, which do not surround the whole embryo, lie only on the animal pole; nevertheless, a blastocoel may be formed by a crevice appearing between the blastomeres and the mass of yolk. The blastomeres then may be arranged as a…
Read More
prenatal development
Cleavage and blastulation
…blastocyst; its cavity is the blastocoel.
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…blastocyst; its cavity is the blastocoel.
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