Mesoderms

Part of speech: noun

Definitions

1. The layer of cells in a developing embryo situated between the ectoderm and endoderm, giving rise to muscles, bones, and connective tissues
2. A cellular layer found in embryos that contributes to the formation of organs such as the heart and kidneys, as well as skeletal systems
3. The middle germ layer in embryonic development responsible for generating various structures including the circulatory system and muscle tissue

Etymology: Mesoderms is simply the plural of "mesoderm," the name for the middle of the three primary germ layers that form an embryo, sitting between the outer ectoderm and the inner endoderm. The singular is the term that matters, and it is built from two Greek elements: "meso-," meaning "middle," and "-derm," from Greek "derma," meaning "skin." Put together, the name describes a layer of tissue that is literally the "middle skin" of the developing body. The plural form appears when biologists discuss more than one such layer, which is most often the case in comparative work across animal groups. Animals with bilateral symmetry all develop three layers, so the plural is useful when comparing their embryos. The term itself is a modern scientific coinage from classical roots, not an ancient word.