Which organ is derived from the mesoderm layer of the gastrula?

the answer is the germ layer

Mesoderm gives rise to muscles, bones, the heart, circulatory system, and internal sex organs.

Explanation:

The mesoderm is a germ layer that forms during gastrulation and is formed in between the ectoderm and endoderm.

The mesoderm gives rise to muscle, cartilage, bone, connective tissue, bone marrow, blood, lymphoid tissue, and to the epithelia of blood vessels, lymphatic vessels, genital ducts, body cavities, ureters, sex organs, adrenal cortex, kidneys, and certain other tissues.

Thus, mesoderm gives rise to muscles, bones, the heart, circulatory system, and internal sex organs.