principal piece meaning in Chinese

主段

Using indirect immuno - fluorescein staining method , the localization of sp - 10 , tmdc - iii and aeg on human , mouse , rabbit , pig , bull sperm was observed under confocomicroscopy . it was found that antigens sp - 10 and aeg express on acrosome of all kinds sperms , supporting their roles in sperm - egg fusion . it was firstly described that tmdc - iii express mostly on the equator , neck and some part of tail of human sperm , on the acrosome of mouse and bull sperms , on the acrosome and neck of pig sperm , on the head , neck , and middle piece , principal piece of tail of rabbit sperm
利用间接免疫荧光法对aeg 、 sp - 10 、 tmdc -蛋白在人、小鼠、兔子、猪、牛精子上进行了精确定位， aeg 、 sp - 10在顶体部均有表达，确证了它们与精卵融合有关：首次对tmdc -蛋白在人、小鼠、兔子、猪、牛精子进行了精确定位，它主要存在于人精子尾部主段，小鼠和牛精子顶体，猪精子顶体和颈部，兔精子头部、颈部和尾部的主段及尾段。