Four-cell embryo. Light micrograph of an early, primitive stage of the human embryo, composed of only four cells. Each cell is called a blasto- mere.

---

Four-cell embryo. Light micrograph of an early, primitive stage of the human embryo, composed of only four cells. Each cell is called a blasto- mere. Granular cytoplasm can be seen inside the cells, and each has a central nucleus. Sperm with tails are visible around the embryo; these sperm were unsuccessful in reaching the egg in time to fertilise it. This embryo is a product of in vitro fertilisation (IVF), that is artificial fertilisation in the laboratory. At the four-cell stage the embryo has divided twice by mitosis, and must grow further before it can implant in the uterus.

---

Size: 3647px × 2480px
Photo credit: © PHILIPPE PLAILLY/SCIENCE PHOTO LIBRARY / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: 4-cell, blastomere, body, embryo, human, ivf, light, micrograph, stage