Dictionary.net

The cell nucleus; mesoplast.

The cell nucleus; mesoplast.

The middle germinal layer of the embryo, lying between the hypoblast and the epiblast and derived from the endoderm and ectoderm. The greater part of the body (skin, connective tissue, bone, muscle, and excretory organs) is derived from the mesoblast.

The middle layer of the primitive embryo.

The middle layer of three in the embryo developing the structures of the skin, connective tissue, bones, muscles, organs of excretion and internal genitals.