Epithelial cells are one of the major cell types in the embryo.  They are tightly connected to each other in sheet or tube structures.  

Epithelial Cells

Mesenchymal cells are one of the major cell types in the embryo.  These cells are either loosely connected or unconnected to each other in sheet or tube structures, and they can function in independent units.  

Mesenchymal Cells

Michigan State University

A developing organism before it hatches or is born.  

Embryo

Barresi, M. J., &amp; Gilbert, S. F. (2020). Developmental Biology (12th ed.). New York: Sinauer.

Developmental Biology (12th ed.)

The stages of development between fertilization and hatching.  These stages include:

- fertilization
- cleavage
- gastrulation
- organogenesis
- larval stages
- maturity
- gametogenesis

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