The inner, more permanent part of a cell's protoplasm, especially in protozoans, distinguished from the outer ectoplast.
From Greek endo- 'within' + plastos 'formed, molded.' Developed in the 19th century to describe the internal protoplasmic core of single-celled organisms.
Early biologists studying amoebas and other protozoans used endoplast and ectoplast to describe what they saw under microscopes, long before we understood that both are just different zones of the same cytoplasm.
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