Question

Mesoderm is formed through invagination of
A. Ectoderm
B. Endoderm
C. Inner mass of cells
D. Primitive streak

Answer 1

Hint: There is the formation of the primitive streak that was found in the blastula stage. Bilaminar layer is formed due to the slight invagination of the inner cell mass. Between the layers and mesoderm the movement of the primitive streak of the cell occurred. Bilateral symmetry in the animals formed by primitive streak.

Complete answer:
Between the endodermal tissues and ectodermal walls mesoderm generates the all organs. And the trunk mesoderm of a neurula stage embryo divided into the four regions such as lateral plate mesoderm, paraxial mesoderm, intermediate mesoderm and chordamesoderm.
By the third week paraxial mesoderm differentiates and begins divided into cuboidal bodies. And on each side of the neural tube mesoderm are located. And in the fifth week 42-43 pairs of somites are present and help to form the distinct surface of elevations on the embryo. During the somite period the first appearance in the future occipital region and then developed in the craniocaudal. After all the process in the somite associated musculature and axial skeleton are rises. And obtained the adjacent dermis of the skin. In the somite’s subsequent pairs formed in the craniocaudal sequence and appeared at the short distance caudal to the cranial end of the notochord.

Therefore the correct option is (D).

Note: Urogenital system, heart, bone connective tissue and muscles made the form of mesoderm. Triploblastic animals developed visceral organs such as intestines and stomachs due to the evolution of the mesoderm rather than retaining the open digestive cavity activities of the diploblastic animals.