Developmental Anatomy

Stage 4: Lab Manual - Horizon 4


  • Length 0.1 -0.2 mm.
  • The above specimen is the blastocyst of the Macaque monkey.
  • Stage 4, the onset of implantation, is reserved for the attaching blastocyst.
  • Implantation includes:
    • a. Dissolution of the zona pellucida, and contact and attachment (adhesion) between the blastocyst and endometrium.
    • b. Penetration.
    • c. Migration of the blastocyst through the endometrium.
  • Ovulation age: 5 - 6 days

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Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.
Published by Carnegie Institution of Washington, Publication 637. 1987.

Stage 4 (PDF 27 KB)


QUESTION: What are the three parts of implantation?