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1. A blastomere of intermediate size, larger than a micromere but smaller than a macromere.
2. The middle zone of the mesoderm of a chordate vertebrate embryo, from which excretory tissue develops.
(Physiology) a blastomere of medium size that is formed by certain types of cleavage
mes•o•mere(ˈmɛz əˌmɪər, ˈmɛs-, ˈmi zə-, -sə-)
1. a blastomere of intermediate size between a micromere and a macromere.
2. the intermediate zone of the mesoderm.