CBSE Class 9 Answered

The mesoderm is the middle of the three primary germ layers of the embryo, lying between the ectoderm and the endoderm. It gives rise to the connective tissue, bone, cartilage, muscle, blood and blood vessels among others.

Endoderm is the innermost of the three germ layers in the embryo. It comes from the inner cell mass of the blastocyst and gives rise to inner tissues and organs such as lung, respiratory tract (except the nose), the digestive tract, bladder, and urethra.

The dorsal nerve cord is one of the embryonic features unique to chordates. It is a dorsal, hollow tubular cord of nervous tissue in chordates.

This cord consists of a bundle of nerve fibers which runs down the back. It lies dorsal to the notochord. The dorsal nerve cord is later modified into the brain and spinal cord.