mesomere

noun Embryology.

1. a blastomere of intermediate size between a micromere and a macromere.
2. the intermediate zone of the mesoderm.

n.

1. A blastomere of intermediate size that is larger than a micromere but smaller than a macromere.
2. The middle zone of the mesoderm of a chordate embryo, from which excretory tissue develops.