A middle layer of tissue in a developing animal embryo which will eventually become the muscles and other connective tissues, the blood vessels and blood cells (if any), and various other organs, structures, and systems (depends on the organism). Animals with this layer of tissue as an embryo are known as triploblastic animals, which includes all animals except for sponges, placozoans, jellyfish, and comb jellies.

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From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.

Mes"o*derm (?), n. [Meso- + Gr. skin.] Biol. (a)

The layer of the blastoderm, between the ectoderm and endoderm; mesoblast. See Illust. of Blastoderm and Ectoderm.

(b)

The middle body layer in some invertebrates.

(c)

The middle layer of tissue in some vegetable structures.

 

© Webster 1913.