mesoderm (mesoderm)

[ cous, vascular, and serous layers. Most of the body of every metazoan animal is derived from the mesoderm. When the embryo becomes four-layered, as it usually does, this state results from the splitting of the mesoderm into an inner visceral and an outer parietal layer, called respeсtively splanchnopleural and somatopleural, or involuntomo tory and vol unto motory. 2. In bot., the middle layer of ti ue in the shell of the spore-case of an urn-mo . mesodermal (mes'ō-der-mal), a. [