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day 1
The start of fertilization of the zygote and the beginning of the secretory phase. The fusion of haploid gametes, egg and sperm, to form the diploid zygote. The secretory phase is the uterine tissue regrowth is completed in preparation for the possibility of pregnancy and the implantation of a fertilized egg. -
Day 4
The blastocyst is hatching, it contains the inner mass cell and the blastocoel. The zona pellucida is disappearing, and the epiblasts and hypoblasts is surrounded by the trophoblasts. -
day 7
The embryo in the uterus completes implantation during this stage. The trophoblast cells start to multiply. Syncytiotrophoblast cells continue to invade the maternal endometrium and cytotrophoblast cells form clumps to form sites of chorionic villi formation. -
day 8
The extraembryonic cavities begin to form. The bilaminar embryonic disc from when the epiblast and hypoblast forms from the inner cell mass. Leading to the start of the gastrulation stage. -
day 16
Gastrulation is continuing, forming the mesoderm which is in the middle of the ectoderm and endoderm. The primitive streak forms on the ectoderm to move migrating cells between ectoderm and the mesoderm. Forming the neural plate (in ectoderm) and the notochord (in mesoderm), which allows for the embryo to fold. -
day 37
The ectoderm forms the sensory placodes, lens pit (D-shaped formation), otocyst, nasal pits moved ventrally, fourth ventricle of brain. The mesoderm forms the heart prominence. Ears begin to develop as the otic walls thicken in appearance. The spinal cord is more distinct. -
day 56
Eyelid, eyes, nose, mouth, limbs, elbows, and separated toes are now formed by day fifty-six. The hands are extended in front the the body. The external genitalia is not developed to detect the gender.
