Brief note on gastrulation in frog

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Gastrulation refers to the series of changes that takes place during embryonic development covering the single layered blastula to a two-layered embryo called gastrula. During gastrulation mass migration of formative movements and rearrangement of cells takes place with formation of presumptive areas of blastula. Several changes or processes taking place simultaneously during gastrulation.

Gastrulation in Frog is as Follows:

Node of cleavage holoblastic, complete and unequal.

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Blastula. It is true blastula, hollow with distinct blastocoels.

Presumptive Areas:

Grey crescent from presumptive mesoderm and presumptive notochord, unpigmented posterior half constitute presumptive endoderm. Anterior pigmented half is presumptive ectoderm.

Gastrulation:

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(a) Gastrulation takes place much after the eggs are laid.

b) Epibolic outgrowth of micromeres over micromere takes place.

Near Grey crescent in the presumptive area of endoderm a depression called blastopore is formed, with lips.

Yolk plug formed.

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Invagination of endoderm takes place as megameres or future endoderm cells migrate towards blastopore and sink inside.

Future notochordal cells turned inside round the dorsal lip of blastopore celld as involution.

Ingression or sinking down of cells does not take place further.

Future mesodermal cells roll inside over the lateral lips and mesoderm of ventral side rolls over so that blastopore is obliterated.

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Megamers directly form endoderm during invagination.

Earlier crescentic grove gradually impushed forming a new cavity called archenteron or primitive gut, which opens outside through blastopore.

Completed Gastrula of Frog Shows:

Blastocoels in completely obliterated.

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Archenteron well developed opens through blastopore.

Root of archenteron is made by notochordal cells sides of archenteron made by mesodermal, floor of archenteron formed by yolky endoderm.

Outer layer of pigmented cells consists of ectoderm and neural plate.

No sign of primitive streak found.

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