The different stages of embryonic development of sheep embryos produced in vitro. A, Matured oocyte (the arrow = 1st polar body); B, Zygote (the arrow = 2nd polar body); C, 2 cells stage; D, 4 cells stage, € 8 cells stage; F, 16 cells stage; G, Morula stage; H, early blastocyst I, expanded blastocyst; J, hatching blastocyst; K, hatched blastocyst; L, blastocyst on day 7 stained with Hoechst.