Theiler Stage 1 - One-cell eggFertilizedone-cellstageegg(embryo),zonapellucidapresent(shownin red).0-0.9dpc(range0-2.5)Scalebarin micronsTheiler Stage 2 - Dividing eggDividingeggstage,zonapellucidapresent(shownin red).Firstcleavageoccursat about24hours.1 dpc(range1-2.5)2-4cells.Scalebarin micronsTheiler Stage 3 - MorulaFour-to 16-cellstageembryosfromearlyto fullycompactedmorula.Zonapellucidapresent(showninred).Embryosin theoviducttowardsutero-tubaljunction.2 dpc(range1-3.5)4-16cells.Allscalebarsin microns.Theiler Stage 4 - Blastocyst (ICM apparent)Embryoprogressesfrommorulato theblastocyststillwithinthezonapellucida(showninred).Thereisearlyevidenceof theblastocoeliccavity.3dpc(range2-4)16-40compactedcells.Allscalebarsin microns.Intheblastocyststage(zona-intact)thereis adistinctinnercellmassandan outerlayeroftrophectodermcells.Usuallylocatedin theuterinelumen.Theiler Stage 5 - Blastocyst (zona-free)Blastocy st(zona-free),invariablylocatedwithintheuterinelumen.4dpc(range3-5.5)Scalebarin micronsTheiler Stage 6 - Attachment of blastocy stBlastocy stsimplants,firstevidenceofembry onicendodermcellscoveringtheblastceolicsurfaceoftheinnercellmass.4.5dpc(range4-5.5)WitschiStage8(rat)CarnegieStage4(human)ScalebarTheiler Stage 7 - Implantation and formation of EggCy linderEctoplacentalconeappears.Rapidincreasein thenumberof innercellmasscellsleadingtotheformationoftheepiblastwithsubsequentgrowthto formtheeggcylinder.Theproximalor visceralcells(oppositesidefromthetrophoblasticcap)arecuboidalin shape.Primaryendodermlinesthemuraltrophectoderm.5dpc(range4.5-6)WitschiStage10(rat)CarnegieStage5(human)ScaleTheiler Stage 8 - Differentiation of egg cylinderImplantationsite2x3mm.Thematernaltissueisinvadedbytrophoblast(primary)giantcellsandtheectoplacentalconeisinvadedbymaternalblood.Differentiationof theeggcylinderintoembryonicandextraembryonicregionsandtheformationof theproamnioticcavity.Reichert'smembrane,w...
