Types of mitochondria observed in oocytes of mammalian species. A: Round (from pig). B: Elongated (from pig). C: Round with peripheral cristae (from pig). D: Round mitochondria with electron-dense granules inside (from cattle). E: Round mitochondria arranged as "string of pearls" (from bitch). F: Hooded mitochondria (from cattle). G: Pleomorphic mitochondria with cristae arranged parallel and close to the outer membrane (from goat).