midpiece
/ˈmɪdpiːs/noun
1Chiefly Biology. A middle section or part of a structure, organism, etc.
2 Cell Biol. A region of the spermatozoon located behind the neck and ensheathed in closely-packed mitochondria.
3 Immunology. A component of complement identified in the euglobulin fraction (consisting chiefly of the first component, C1). Now historical.
Origin
Late 19th century; earliest use found in American Naturalist. From mid + piece.