“缺环”就是“缺失环节”的简称。http://www.baidu.com/s?ie=gb2312&bs=%D3%A4%B6%F9%B2%B9%B3%E4%CE%AC%C9%FA%CB%D8&sr=&z=&wd=%C8%B1%BB%B7&ct=0&cl=3&f=8