The fertilzed eggs of Tegillarca granosa stained with DAPI were observed by f iuorescent microscope. The result show s that the mature eggs were at metaphase of first meiosis. After sperm penetrating, the eggs released their first and second po lar bodies and f inished their meiotic division. Some first polar bodies divided into two small cells. The eggs Tegillarca granosa became monospermic. While the male and the female pronucleus were produced, they expanded to their maximal size. And the male pronucleus moved to the female pronucleus during the period of associating of the two pronucleus.