A) endoderm
B) mesoderm
C) etoderm, endoderm
D) ectoderm, mesoderm, endoderm
Correct Answer: D
Solution :
Gastrulation is a nicely integrated, dynamic process; which is controlled largely by intrinsic (i .e, autonomous) force bound up in the specific physico-chemical conditions of the various presumptive organ-forming areas of the late blastula and early gastrula. These internal forces in turn are correlated with external conditions. One of the important intrinsic factor involves the so called organization. Gastrulation as the name implies, has to do with the formation of primordial gastric or gut cavity called archenteron. In the majority of cases archenteron is entirely separate from the blastocoel right the beginning of its formation. The formation of gastrular cavity or archenteron involves the setting apart of two of the three primordial germ layers, which are the ectoderm and the endoderm. The ectoderm is the outer layer while the endoderm lining the archenteron, From these layers all higher animals start their differentiation. But this however, is not quite correct because a third layer named mesoderm is also supposed to present which is derived either from ectoderm or from endoderm or from both. Therefore, the one from which the third is derived in cases where the origin is clear, often temporarily termed as mesectoderm of mesentoderm as the case my be. Another term epiblast is usually be applied for outer layer while for the inner layer one can also use the term hypoblast. After that each of these layers can be referred to by its definite name, ectoderm, mesoderm and endoderm.
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