Indicator of sta of gastrulation is the formation of ?

Ans. is 'c' i.e., Primitive streak Gastrulation, the most characteristic even occurring during Yd week of gestation, establishes all 3 germ layers (ectoderm, mesoderm & endoderm). It conves the bilaminar embryonic disc into a trilaminar, and is the beginning of morphogenesis. Ectoderm is first and mesoderm is last to develop.1" sign of gastrulation is appearance of primitive streak on the surface of epiblast. The primitive streak appears caudally in the median plane on dorsal aspect of the embryonic disc. So now it's possible to identify the embryo's craniocaudal axis, its cranial and caudal end, its dorsal and ventral surfaces, and its right and left sides.